Windows support: first attempt

Hello everybody out there ~~using~~ trying to use Meteorite on Windows

I've tried to start Meteorite on Windows and, not surprisingly, it didn't work at all. My computer's background: npm, msys, meteor and git are installed (everything is in the PATH). I use half-official meteor for Windows, the one from 'bootstrap script', not MSI.

I've investigated the problem a little and I found three things that prevent `mrt install`/`mrt update` from running correctly on my system:

1. `git clone` do not create several nested folders, as it do on Linux. Well-known, see https://github.com/sbt/sbt/issues/895 .
2. `meteor` on Windows is not an executable, it's a script called `meteor.bat` - big difference, as only executables can be ran directly, in contrast with linux. So, usual `spawn` fails to find `meteor.exe`. Well-known too - https://github.com/joyent/node/issues/2318
3. Unlink behaves differently on Windows and Linux with read-only files ( https://github.com/joyent/node/issues/3006 ). On Linux, they're normally deleted. On Windows, function fails with `ENOPERM`.

I've fixed all of them locally and reported number three to `wrench-js`: https://github.com/ryanmcgrath/wrench-js/issues/70 .

This branch with fixed `wrench-js` (as I've suggested in the last issue) works OK on Windows. At least, I can perform `mrt install`, `mrt update` and `mrt create`.

It would be great to get some feedback from another Windows users and to get thoughts of Meteorite authors on this issue.