Add the fixed width C99 types from stdint.h

Add the fixed width C99 types from stdint.h

C99 has standard types for fixed width signed and unsigned integers.
This adds types to giscanner to map them to the glib equivalent types.

stdint.h also has other types to specify specify sizes with at least a
certain number of bits, the fastest type with at least some number of
bits, a type big enough to store a pointer and a type containing the
most number of bits. These don't map well to glib types so I have
ignored them.

https://bugzilla.gnome.org/show_bug.cgi?id=674796