parsing of tokens that have to be of n length to be valid

In the current code, the lexer only checks the first char to consider it a token and apply `is_md_token` on it and then uses `peek_type()` on it to make the whole token.

This is an issue when we run into tokens that have to be a certain length such as ` ``` ` to be valid.

For this is i hope to implement a new system in the lexer where we have a function with the following signature `peek_n(FILE * fp, char base, int n)`.

This will allow us to lex tokens that also have to be of a certain length.