Windows Support

This PR adds support for building and running a release on Windows.

Includes:

* `bootstrap.cmd` to compile and escriptize relx on Windows since Make isn't available
* `priv/templates/bin_windows.dtl` to render a batch file for starting a release
* `priv/templates/extended_bin_windows.dtl` to render a batch file for managing the release as a Windows service

It also includes additions to `rlx_prv_assembler` that outputs a start_erl.data file to be compatible with the `start_erl.exe` program as well as handling other special cases for the Windows environment (file extensions, rendering the right templates per os, etc.).