Simpler names for integer types.

* New typedefs uint8, uint16, uint32, uint64
  replace unsigned char, std::uint16, std::uint32, std::uint64.

* New typedefs int16, int32, int64
  replace std::int16, std::int32, std::int64.

* New typedef int8, not yet used.
  (Most instances of signed characters are just characters.)