Move bootstrap to module

This fixes on Windows #222. The unix shell script still needs to be updated.
Another minor change is the rockspec, using per platform overrides, so the batch and unix scripts only get installed where appropriate (please test this on Unix and Mac!)

I moved the bootstrap script into the module tree. Initially I tried to use the `lua` `-e` option to load the module, but when `-e`executes, the commandline is not available yet to Lua scripts, so that didn't work.
The alternative I implemented was a 1 line temporay Lua script that executes the loading of the bootstrap module.

Todo:

 - update unix shell script to create/use a temporary Lua script
 - test the per platform overrides in the rockspec on unix and mac