Make Peanut-GB strictly C89

[deltabeard]

This means:

• Not declaring variables in for-loop initialiser.
• Not declaring variables in the middle of a block.
• Not using stdint.h.
• C++ style single-line comments.

Peanut-GB must compile with Visual C++ 6 (VC6).

[deltabeard]

2471c89d2ada67dfffe676c5509db13ea7cf21da Compiles with MSVC 2. Not strictly C89 compliant though, but I'm not sure it's necessary and useful features, such as bitfields of various types, and anonymous structs aren't available in C89 but are still supported in ancient compilers like MSVC 2.