Changelog:

• Minor bugfixes.

• Stable API
• Support for pkg-config

• Rewrote bfand(), bfor() and bfxor() to accept variable number of arguments.

• Fixed memory leaks in shift_ip() and bfnormalize().
• Fixed bugs in uint64tobf() and bftouint64().
• Rewrote uinttobf(), uinttobf_ip(), bftouint**(), bftouint**_ip(),
  long2bf(), long2bf_ip(), bf2long(), bf2long_ip().
• Replaced ll2bf(), ll2bf_ip(), bf2ll() and bf2ll_ip() with macros (assume
  long long is always same length as uint64_t).
• Minor optimization in shift_ip() and bftouint32().
• Removed internal functions from the list of exported symbols.
• Rewrote tests so they do not rely on internat functions from bitfield library.