deps: Add path-browserify package as local dependency

This module is independent from npm dependencies and live in `vendor`
directory. As browser only support importing ES modules, I've changed a bit
the module exports to use ESM instead.

The `path-browserify` package matches with Node.js v10.3 API.

Author: mitsuki31

vendor/path-browserify/.github/FUNDING.yml

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+# These are supported funding model platforms
+
+github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+patreon: # Replace with a single Patreon username
+open_collective: # Replace with a single Open Collective username
+ko_fi: # Replace with a single Ko-fi username
+tidelift: npm/path-browserify
+community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
+liberapay: # Replace with a single Liberapay username
+issuehunt: # Replace with a single IssueHunt username
+otechie: # Replace with a single Otechie username
+custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']

vendor/path-browserify/.travis.yml

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+language: node_js
+sudo: false
+node_js:
+  - "10"
+  - "9"
+  - "8"
+  - "6"
+  - "4"
+  - "iojs"
+  - "0.12"
+  - "0.10"
+  - "0.8"
+before_install:
+  # Old npm certs are untrusted https://github.com/npm/npm/issues/20191
+  - 'if [ "${TRAVIS_NODE_VERSION}" = "0.6" ] || [ "${TRAVIS_NODE_VERSION}" = "0.8" ]; then export NPM_CONFIG_STRICT_SSL=false; fi'
+  - 'nvm install-latest-npm'

vendor/path-browserify/CHANGELOG.md

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+# path-browserify change log
+
+All notable changes to this project will be documented in this file.
+
+This project adheres to [Semantic Versioning](http://semver.org/).
+
+## 1.0.1
+* Fix a duplicate test name.
+* Tweak LICENSE text so Github can recognise it.
+* Tweak LICENSE text to include the year and author.
+* Add security policy file.
+
+## 1.0.0
+This release updates to the Node v10.3.0 API. **This change is breaking**,
+because path methods now throw errors when called with arguments that are not
+strings.
+
+* Add `path.parse` and `path.format`.
+* Add `path.posix` as an alias to `path`.
+* Port tests from Node.js.

vendor/path-browserify/LICENSE

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+MIT License
+
+Copyright (c) 2013 James Halliday
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/path-browserify/README.md

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+# path-browserify [![Build Status](https://travis-ci.org/browserify/path-browserify.png?branch=master)](https://travis-ci.org/browserify/path-browserify)
+
+> The `path` module from Node.js for browsers
+
+This implements the Node.js [`path`][path] module for environments that do not have it, like browsers.
+
+> `path-browserify` currently matches the **Node.js 10.3** API.
+
+## Install
+
+You usually do not have to install `path-browserify` yourself! If your code runs in Node.js, `path` is built in. If your code runs in the browser, bundlers like [browserify](https://github.com/browserify/browserify) or [webpack](https://github.com/webpack/webpack) include the `path-browserify` module by default.
+
+But if none of those apply, with npm do:
+
+```
+npm install path-browserify
+```
+
+## Usage
+
+```javascript
+var path = require('path')
+
+var filename = 'logo.png';
+var logo = path.join('./assets/img', filename);
+document.querySelector('#logo').src = logo;
+```
+
+## API
+
+See the [Node.js path docs][path]. `path-browserify` currently matches the Node.js 10.3 API.
+`path-browserify` only implements the POSIX functions, not the win32 ones.
+
+## Contributing
+
+PRs are very welcome! The main way to contribute to `path-browserify` is by porting features, bugfixes and tests from Node.js. Ideally, code contributions to this module are copy-pasted from Node.js and transpiled to ES5, rather than reimplemented from scratch. Matching the Node.js code as closely as possible makes maintenance simpler when new changes land in Node.js.
+This module intends to provide exactly the same API as Node.js, so features that are not available in the core `path` module will not be accepted. Feature requests should instead be directed at [nodejs/node](https://github.com/nodejs/node) and will be added to this module once they are implemented in Node.js.
+
+If there is a difference in behaviour between Node.js's `path` module and this module, please open an issue!
+
+## License
+
+[MIT](./LICENSE)
+
+[path]: https://nodejs.org/docs/v10.3.0/api/path.html