Cleanup basic int type usage and type naming

I have 3 issues with the custom types specified here: https://github.com/darktable-org/rawspeed/blob/develop/src/librawspeed/common/Common.h#L35-L41

1. Their naming contains the size info twice, e.g. ushort16 and the names (strings) are not equally long.

I like to suggest two alternative variants:

• Rust names (u32, i16, etc.)
• <cstdint>: http://en.cppreference.com/w/cpp/types/integer

I'd prefer the short Rust names, especially because the std names are longer than what we have right now and the _t postfix looks very 'c-ish' to me. I'd also suggest to keep the word byte and even use that term as a type name for the unsigned char case. That name even almost made it into c++17. The idea is to distinguish between simple data bytes and characters (as in bits of a string).

2. The usage of the uint32 for offets/sizes is 'non-standard'

I'd like to go over the interfaces that I touched and simply use size_t for that, even in the cases where I introduced the size_type name that can be found in the std:: containers. I always found that part a bit 'over engineered'.

3. Their definition is potentially wrong (depending on the data model, see http://en.cppreference.com/w/cpp/language/types). E.g. the tiff code breaks if 'unsigned int' would be 16bits wide. This should be non-controversial and is trivial to fix.

@LebedevRI What is your opinion on 1) and 2)?

Start with the custom type definitions in src/librawspeed/common/Common.h at lines 35–41, then trace their use in interfaces and the TIFF code. Compare the proposed naming alternatives, review offset and size parameters for size_t usage, and check the definitions against C++ data-model guarantees. Done means the chosen type naming, usage, and definitions are applied consistently.