Fix makefile to always use tools path
Fix capsens performance by manually unrolling loop.

  Automatic unrolling of loops doesn't work now the array sizes are
  static variables and not #defines. This fix manually unrolls the main
  port reading loop which assumes that the number of samples is divisible
  by 4.
Merge pull request #3 from davelxmos/perf_fixes

Makefile fix + performance fix