added decode function to handle special characters
added new token types
added to_letter in utils
modified lexer to return token value and handle break character
modified main to print token value
added new states for automata
added C keywords and function to check if string is keyword
fixed defining C_keywords
removed token.h from lexer.h
defined KEYWORD_T in token.h
added if to change token type if value is keyword
added keywords in makefile
added some C code for test