cpu stats for darwin
Merge branch 'master' of github.com:square/prodeng into s-darwin

* 'master' of github.com:square/prodeng:
  cleanup of metrics library
Per PID statistics for macosx
works now with basic information
formatting
functional cpu/mem/per-pid stats for darwin
move os specifit implementation to osmain

* cleaner interface for processstat i guess
few modifications to make things work
formatting
make free() reflect memory pages that are free under memory pressure
add purgeable to free
Merge pull request #35 from square/s-darwin

Add basic support for MacOSX (darwin)