This attempts to organize all needed items and places appropriate defines
in a single location. Redundant comparisons/defines were removed when noticed.
A few caveats, however:
* This may be better targeted towards the 5_1_0 branch instead of master right now.
* Cmake will run a little slower on configuration/generation now. That's due to the sanity checks it runs.
* There are some more checks to be added later, but this should be a solid start.
Thanks to the [libical](https://github.com/libical/libical) project for inspiration.
There are two targets you may not be familiar with, `install` and `package`.
* For Linux, `install` now defaults to `/usr/local`, but you can set it back to `/opt` with `cmake -DCMAKE_INSTALL_PREFIX=/opt` if you wish.
* For Windows, `install` may not work, but this is not a target you would want usually.
* For Linux, `package` has not been tested yet. It will likely create an archive file of what is installed.
* For Windows, `package` will create an NSIS package that can be used to install StepMania. One minor change as a result is that the binary and companion dlls will be placed in `bin` instead of `Program` now, but it makes no difference code-wise.
Mac OS X users: for now, use the `dmg` target instead.
This commit does *not* deprecate the original nsi script yet. The Texture Font Generator program has not been addressed yet.
Jason Felds