Added backslash (line continuation) handling

Added a test, will need to modify it when I support escaped
characters
Refactor, pulling lexer out of parser.c/h

There is a bit of a grey area so I really only extracted
the tokenizer into lexer.c.  I feel the reading all the tokens
into an array for backtracking/seeking and building a
stringdb etc. should be an option and not part of the lexer.