FIX: Removed included Exprtk - now it's compiled as ExprtkWrapper and it's not needed to include the whole header-library.

NEW: Added message.h with message macros MSG_INFO and MSG_DEBUG intended to unify and simplify library output.

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.

FIX: fixed an issue with ExprtkWrapper being incorrectly destryed before being used in the NetworkSum class

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.

MOD: Modified examples and unit tests to account for the changes