Reaction System Solver

First release of reaction system solver consisting of 3 modules:

• a string parser that converts a list of reaction strings into reactant and product stoichiometry matrices.
• a ODE solver that imports the stoichiometry matrices to generate dydt function that can be solved with provided functions (using scipy) or externally.
• a Gillespie algorithm supporting full and optimized updating scheme that imports the stoichiometry matrices, generating copy numbers vs timetrajectories.