support for out of source builds

[lammermann]

Would be great to have out of source building support. Then it would be possible to generate e.g clang and gcc Makefiles in different places and make it easier to test the toolchains. Additionally the sourcetree would remain clean which makes searching and editing the sources simpler.

This should be an easy task by using the location parameter in premake. See http://stackoverflow.com/questions/25385781/premake4-out-of-source-build for example.

[warrenseine]

It should be fairly easy to setup, but the issue might be with the tons of scripts that rely on the actual location of the binaries. Typically, when developing a Minko application other than an example, linking the framework relies on the MINKO_HOME environment variable and the relative location of binaries.

Though I'd totally prefer to avoid bloating the source directory with binaries, it's fine in our current workflow so I don't think we're going to do anything about it anytime soon. If you do find a way to fix this, we'd love to get a PR.