This allows the markdown reader to treat '\begin' (not followed
by an argument) as a raw string rather than erroring out when
it doesn't find a '{'.
Closes#622.
- Removed writerLiterateHaskell from WriterOptions.
- Removed readerLiterateHaskell from ReaderOptions.
- Added Ext_literate_haskell to Extensions. Test for this
instead of the above.
- Removed failUnlessLHS from Shared.
Note: At this point, +lhs and .lhs extension no longer has any effect.
Need to fix.