Code: Refactors MSVC solution.

* Sorts and purges removed headers.
* Also remove redundant `getopt` shim.
* Shares includes between libsass and sassc, using libsass.targets file
  .
* Continues MSBuild when stderr emits output This happens when `git` is
  not available in `PATH` (or not installed) on the target system.

Author: am11