Add the missing Windows SDL libs and upc.exe

These files are shipped with libtcod source and are required to compile libtcod.
Our .gitignore has *.dll and *.exe so these were ignored.

This whitelists the specific files we need.
Add Windows support to tcod-sys' build script
Fix Travis

Travis no longer needs to download the libtcod binary distribution, but it needs
the dependencies to build libtcod.
Update the documentation

This mostly describes how to use tcod-rs with the new build scripts but also
fixes broken libtcod links and adds the missing contributors.