c5 - C in four functions + AST + back-end code generator

An exercise in minimalism.

This branch extends c4.c by adding:

• Abstract Syntax Tree creation
• Back-end code generator function: gen()
• Standard ordering of function parameters on stack
• Native x86 version: c5x86.c
• Various optimizations

Try the following:

gcc -o c5 c5.c  (you may need the -m32 option on 64bit machines)
./c5 hello.c
./c5 -s hello.c

./c5 c5.c hello.c
./c5 c5.c c5.c hello.c