Refactor parseAndDesugar
Refactor parseAndDesugar

In preparation for writing a slightly different version, which does not
do importPrim. This is in order to be able to produce JSON files using
psc-publish for purescript-prim; we need to be able to tell psc-publish
not to add a Prim import, so that we can avoid RedefinedModule errors.

michaelficarra/purescript,michaelficarra/purescript