Add isTokenDelimiter function
Add isVariableNameChar function
Add CLocaleEnvironmentStub class
Add AssignmentParserImpl template class
Add AssignmentParser class
Add CommentSkipper class
Add CommandParser abstract class
Remove mSourceLocation from Command

It seems Command should have SourceBuffer::ConstIterator as a pointer to
the corresponding source location. For now we remove SourceLocation from
Command; we will add ConstIterator (or something else) again in the
future.
WIP: Add SimpleCommandParser class