Use custom parser monad instead of Parsec. It remembers the text which
has been parsed, so it needs not to be reconstructed after parsing.

Operators containing '--' are now handled correctly. '#' triggers
special processing only if it's not a part of an operator, i.e. if
a varsym token is exactly a single '#'.

Backslash-newline pairs in C lexical world are now handled correctly
(removed at an early stage).

Option --keep replaced with --no-compile (stop after writing *.hs_make.c).