Migrate to parser-2.0.0.beta1.

Perform name changes source_map to location, src to loc, to_source
to source, cdecl to casgn, and remove cvdecl.
Use the new parse_with_comments() method in Parser.
Port AsciiComments and LeadingCommentSpace to Parser.
Merge pull request #196 from jonas054/port_ascii_comments

Port ascii comments and leading_comment_space