Codechange: Various C++ cleanups.

[PeterN]

Various cleanups to C++-ify the code:

• Samples is now a std::vector<Sample> instead of std::vector<Sample *>. Samples pointers are not stored anywhere else so there's no worry about its location changing if the vector is reallocated. This simplifies clean up as no pointers need to be deleted.
• Sample data is now stored in a std::vector<uint8_t> instead of a raw pointer allocated with malloc(). This avoids needing to manually free() during clean up.
• Removed typedef std::string string in favour of just using std::string everywhere, and use const std::string & when we're passing an existing string without making a copy.
• Include cstdint, instead of defining uintX_t on Windows.