ast: add FunctionNoProtoType

[mewmew]

c2go is now capable of parsing function types without parameters.

Example C source that is now parsed:
typedef int (*foo)();

Fixes #831.

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This change is 

[mewmew]

Note, c2go is now capable of parsing function signatures without parameters. However, I've not yet figured out how to add type resolution for the produced AST nodes.

When using c2go to parse the following two C source files, the former produces a Go source file without warnings, and the latter produces two warnings related to type resolution.

No warnings in Go output source file

Input C source:

typedef int (*foo)(void);

Output Go code (extract):

package main

type foo func()

Warnings related to type resolution in Go output source file

Input C source:

typedef int (*foo)();

Output Go code (extract):

// Warning (TypedefDecl):  /home/u/Desktop/ccc/a/a.c:1 : Cannot separate function 'int (*)()' : Cannot resolve type '' : probably an incorrect type translation 1
// Warning (TypedefDecl):  /home/u/Desktop/ccc/a/a.c:1 : Cannot resolve type 'int (*)()' : Cannot separate function 'int (*)()' : Cannot resolve type '' : probably an incorrect type translation 1

package main

type foo func()