implement quads
implement quad lists
add utilities for yacc

- New quad_value constants were created.
- New quad for returns that return an operand.
- New quad creation functions for the most used branchs:
  branchs on equal to 0 or 1
initial quad use in lex and yacc
fix unduplicated identifier
free identifier strings
destroy completed quad lists
add quad_value utilities
fix unduplicated quad values
Merge branch 'quads' into dev

Partial implementation of quads.