disable spell check in code blocks

[wsor4035]

see streetsidesoftware/vscode-spell-checker#202 (comment)

for more details #236 (comment)

[appgurueu]

Aha. Seems a bit hacky (parsing Markdown with Regex and all that, also doesn't really translate to inline code as easily, though there's probably a good regex to be found here too by taking plausible usage of spaces into account) but should work reasonably well 👍