Add Any node

To write out any text representation under FileAST node is required
by such program that tries to convert inline function to equivalent macro.

This patch adds Any node which is not relevant to parsing but only to
writing out (via generator).

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>

----

This patch is related to #42 

I hope you like this patch.

The AST-rewrite example is rewritten. The code after the rewrite is now:

```c
#define f(a) ((a) * 2)
/* rewrited function */
void func(void)
{
  y = 2;
}
```