PR: Gibbs Monte Carlo Examples update + output file generation + Input variable container

[Zhaoli2042]

1. added NPTMC Volume move example
2. updated NVT-Gibbs Move example for TraPPE CO2
3. Source code modifications 3.1 added input container struct as a buffer storage to convert any form of input to something gRASPA can read (currently works for force field parameters) 3.2 added variables struct as a bucket for all variables used during the simulation 3.3 small fix for tail-correction, now it should be okay to use tail_correction in force_field_mixing_rules.def for all pairs of interactions 3.4 added Keyword "StructureFactor_Multiplier XXX" to allocate more structure factors (multiplies by initial number of structure factors in three dimensions) for Ewald summation, useful for simulations with volume moves, pre-allocate more space to prevent re-allocation during the simulation
4. Add Output option in keywords, use "SaveOutputToFile yes" keyword in simulation.input to save output data file (RASPA-2 style)
5. Add NPT-Gibbs example