* Always define GEANY_FOO_H to 1 in the header guards
* Always put a G_BEGIN_DECLS/G_END_DECLS guard in every header for
consistency, even private ones where it doesn't matter.
* Always include either <glib.h>, <gtk/gtk.h> or some other header
that will provide G_BEGIN_DECLS before using it. In a lot of headers
that use glib.h and gtk/gtk.h stuff anyway, this resolves an implicit
dependency they had on them being included before that header.
* Always put a comment at the #endif part of the guard so it's
easier to see what it applies to.
* Always use an underscore between the header guard identifier's words
even though the filename doesn't have one.
Most noteworthy change is that all build commands IDs and groups are
now unsigned everywhere negative values aren't explicitly handled with
a special meaning. This should not change anything in behavior, only
makes clear the index won't underflow.
