Important rewrite and optimization

• Fixed WAV file parsing.
• Explicitely unroll some loops
  to enhance encoding speed. Thanks
  to @ckthomas on github for these
  changes!
• Add -funroll-loops to CFLAGS
• Major code cleanup by @zhaoxiu-zeng
  on LingYunZhi/shine.
• Added interleaved API, also contributed
  by @zhaoxiu-zeng
• Bumped ABI to 3.1.0