Add a debug flag

[shubhamugare]

SynCode provides a flag --debug to help debug grammars. This flag will print out the parsed terminals and their corresponding values in generation.
(Refer to this notebook for code example)

For example, consider the following grammar:

start: "foo" "(" ident ")" ";"
ident: [a-z]+

Given the output foo(abc);, the debug flag will print:

--------------------------------------------------
Parsed terminals:
(type: 'FOO', value: 'foo')
(type: 'LPAR', value: '(')
(type: 'IDENT', value: 'abc')
(type: 'RPAR', value: ')')
(type: 'SEMI', value: ';')
--------------------------------------------------