Return empty from EOF parser
Allow parse mapping with function returning reference

The return type will now be successfully inferred if a mapping returns a
reference.
Add skip_line_continuation function
Add skip_line_continuations function
Combine line continuation and char parsers

The line_continued_char.hh file declares the
test_char_after_line_continuations, parse_char_after_line_continuations,
and accept_char_after_line_continuations functions. They are
combinations of the line continuation skipper and char parsers.
Skip line continuations while parsing raw string
Merge pull request #145 from magicant/feature/parser

Skip line continuations while parsing raw string