Report runtime libsass version

[saper]

Currently we give simply what we have in package.info:

function getVersionInfo() {
  return [
           ['node-sass', package.version, '(Wrapper)', '[JavaScript]'].join('\t'),
           ['libsass  ', package.libsass, '(Sass Compiler)', '[C/C++]'].join('\t'),
  ].join(eol);
}

Because I often link to the libsass shared library or (for the official FreeBSD binary) I include the externally-built libsass.a it would be great to know which version we are running at the moment.

Also what about adding a build metadata (+FreeBSD etc.) to the version number for the official binaries?