#23 Add a file-wide documentation

[Anonymous]

Lets say we have a file with several if-deffed
declaration of LOCK_SAVE().
It looks like this:

#ifdef AAA
#define LOCK_SAVE(aaa)....

#elif defined(BBB)
void LOCK_SAVE(ccc)
{
}
#else
#define LOCK_SAVE(xxx) _LOCK_SAVE()
#endif

What we need is a way to document LOCK_SAVE in
one place. This documentation does not
care if LOCK_SAVE is a macro or a function.
Also, it should not require that the actual
declaration follows the sourcedoc comment.
Only one comment with the same name should be
allowed.

Proposal:

@globaltype

Should work as @type, but only one per file with the
same name, ignoring what follows.