Update cmake build system

[ftynse]

With cmake, we compile all the sources twice: first, for the static library, and then, for the shared library. However, cmake 2.8.8 introduced object libraries to avoid such recompilation.

Debug/Release states are hardcoded in the current CMakeLists, but they should rather depend on CMAKE_BUILD_TYPE.

Finally, I do not see the reason behind installing the test suite to /usr/share.

See ftynse/chlore@39ade18 for example file.