ENH: Removed relative paths to 4neuro.h, as it's not needed, when the code is given the proper include directory during compilation.

FIX: Fixed relative paths to headers, so it isn't neccessary anymore to include SRC_DIR when compiling examples / independent apps, which only use lib4neuro.

Rewitten compilation to simplify CMake scripts and to be able to compile examples just linked with 4neuro without being forced to link/include other dependencies.

This reverts commit 24948047.

descent method