lexer: Add Lexer.emitError()

and change TokenError.String() to show the whole payload

Signed-off-by: Alejandro Mery <amery@geeks.cl>
lexer: add Lexer.skip() to trash data

Signed-off-by: Alejandro Mery <amery@geeks.cl>
token: Token.String() don't truncate content

Signed-off-by: Alejandro Mery <amery@geeks.cl>