BSD, OSX, Solaris support

[FreeSlave]

Need to bring this library on these platforms too.

[MarcAntoine-Arnaud]

I start to fix build on OSX.
Can you provide some inputs to support it on OSX ? I can develop it.

[FreeSlave]

Some info about OS X http://stackoverflow.com/a/1911863
Windows and Linux versions are also based on the answers from this page.

[MarcAntoine-Arnaud]

Thanks, I've start to take a look on it, I have implemented information about swap usage.
I'll complete soon with others parameters and submit a new pull request.

[FreeSlave]

Getting per-process CPU usage was added for FreeBSD.