lexer: turn tests to print tokens

Signed-off-by: Alejandro Mery <amery@geeks.cl>
lexer: fix logical error in Lexer.emptyBack()

Signed-off-by: Alejandro Mery <amery@geeks.cl>
lexer: fix usagle of ` vs "

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