[javascript mode] Fix bad indentation below if

Closes #1662
Add another exception to the spanAffectsWrapping hack

And turn the hack off in recent Chrome builds.

Issue #1663
[python mode] add configurability

Can pass extra keywords and builtins lists
[python mode] document new options
[python mode] Add cython mode
[meta.js] fix gfm in meta.js, missing mimetype