Shiny new process class and cleanup of terminal*

[eidheim]

• Can now do for instance "echo test && echo test" on Windows, as the Process class uses sh if compiled with -DMSYS_PROCESS_USE_SH.
• Now attempts to kill child processes of a started process on Windows if any, as far as Windows actually manage to do this.

Tested on MSYS2, OS X and Ubuntu 14.

[eidheim]

Forgot: ready for merge if your tests go through.

[eidheim]

Tested again on OS X, MSYS, Ubuntu 14. And also Debian testing.

[zalox]

Why not use enum directly? In terminal->print() we could add PANGO_WEIGHT_BOLD | PANGO_STYLE_ITALIC for instance.

[zalox]

Saw that this is texttag which doesn't have operator|() overloaded so I guess just ignore this.

[eidheim]

@zalox : If this looks ok, you can merge and pull the changes from cppit/jucipp/master into your branch and #99. In that way we only have to resolve a few conflicts at a time, and it will be easier to find errors in the conflict resolution, if any.

Have tested this PR thoroughly on all platforms.