CMake fixes

[vizzerdrix]

HI
I was trying to add your project to mine and I've met some CMake problems. I've fixed them in my way (I had to keep company standards) and I would like to share it.

Generally, there are three problems.

1. It's impossible to build a project from the directory that is outside of your source code tree. I've fixed path to your cmake_scripts directory, it's a trivial change (359058f)
2. My project configuration forbids to place any files outside of PROJECT_BINARY_PATH, in past, that kind of files causes a lot of headaches because of naming collisions. Our build dir contains many subprojects and sometimes some of them try to put files with the same names in CMAKE_BINARY_PATH. That's why the global policy works as works. (5adf687)
3. We also cannot break the shadow build idea. All generated, compiled, build-time-created files shall be placed in PROJECT_BINARY_PATH. I've removed LINK_DIRECTORIES line because I don't know why is needed in that context but maybe I'm wrong and it's needed, however.

So thanks for sharing your library, feel free if You want to use (or not :-) this pull request.

PS: I'm not CMake specialist, frankly speaking, I hate it, so my changes may not be the best.
Michal