[ENH] [FIX] Implemented support for ACSF coordinates and automatic network creation from XYZ molecule dataset.

[NEW] [DEL] Removed main.cpp and 'test_cases' executable and created dev_sandbox.cpp and 'dev_sandbox' target instead.

ENH + NEW: Implemented the data normalization funcionality to DataSet. Created a new class NormalizationStrategy.

ENH: Only classes belonging to API are now contained in 4neuro.h. All those classes were enclosed in 'lib4neuro' namespace.

ADD: added preliminary version of gradient calculation vie backpropagation, added supporting methods to error classes and learning algorithms utilizing gradient calculation

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

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.

-added an example testing multi-network error function

- Added preliminary connection classes with neural network class able to evaluate inputs via the feed-forward method.
- Added a test case for validating feed-forward capabilities of our networks