Don't pass -optl-pthread on Windows.
Add Null constructor to JSON; to be fully tested

Conflicts:
	lib/stdlib.js
	libraries/haste-lib/src/Haste/JSON.hs
Add Null constuctor to encodeJSON
Handle POST ajax queries properly as a form submission

Conflicts:
	lib/stdlib.js
	libraries/haste-lib/src/Haste/Ajax.hs