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.

ENH: Added -fPIC option to the linux_gcc_build_x64_debug.sh, so the Boost libraries will be always compiled as a position independent code, even if they're static. It makes possible to link them to the shared library lib4neuro.

FIX: FindBoost.cmake now sets the variable Boost_LIBRARIES, which contains libraries' names, but it also makes them targets, so the other applications can be linked against them. The variable BOOST_LIBRARIES was removed.

FIX + NEW: Trying to fix CI + added new compilation script for CI Ubuntu with dependencies stored in system paths.

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.