Can't save unsigned integers

[CelticMinstrel]

I tried saving a uint64_t and got a "Can't serialize type" exception. Even if you can't support uint64_t (not sure if the plist format can represent it fully), it seems pretty easy to at least support smaller unsigned integer types, since they can be exactly represented by int64_t.

Note: Using the uint64_t works when I read plists with <Foundation.h>, but I have no idea if it silently introduced problems.

[CelticMinstrel]

It appears that the <Foundation.h> API can and does correctly save unsigned integers greater than 2^63-1, so perhaps it would indeed be good to support uint64_t in the library. I could even send a patch (or pull request) for it.