add adapter for formstate (#28)

* add adapter for formstate

* eliminate duplicated code

* property origin for xified state

* update README

* use state.hasError instead of state.error

* v1.2.0

* remove nouse comment

Author: nighca

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "formstate-x",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "description": "Extended alternative for formstate",
   "repository": {
     "type": "git",
@@ -33,6 +33,7 @@
   "devDependencies": {
     "@types/jest": "^25.2.1",
     "@types/node": "^12.7.12",
+    "formstate": "^1.0.0",
     "jest": "^25.2.7",
     "mobx": "^5.15.4",
     "ts-jest": "^25.3.1",

package.json

@@ -0,0 +1,29 @@
+# formstate adapter
+
+This module provides a [formstate](https://github.com/formstate/formstate) adapter, with which you can use formstate state in formstate-x `FormState` like this:
+
+```ts
+import * as fs from 'formstate'
+import { FormState } from 'formstate-x'
+
+// the adapt method
+import { xify } from 'formstate-x/esm/adapter'
+
+// formstate FieldState or FormState
+const stateA = new fs.FieldState(1)
+const stateB = new fs.FormState({ ... })
+
+// formstate-x FormState
+const formState = new FormState({
+  a: xify(state),
+  b: xify(stateB)
+})
+
+// you can use the form state as usual
+console.log(formState.value)
+const result = await formState.validate()
+```
+
+It is helpful when migrating your project from formstate to formstate-x. Instead of rewriting all your input / field components at once, you can do it one by one. The adapter makes it possible to use formstate-based input / field component in a formstate-x-based form / page component.
+
+**NOTE: [`FormStateLazy`](https://formstate.github.io/#/?id=formstatelazy) is not supported yet.**