Update read-the-docs documentation

[ClaraBuettner]

The read the docs description will be extended in preparation of the next release.

Planned changes:

• adapt structure to new file structure (K)
• add publications (K)
• check and update existing texts and explanations (K)
• write 'Contributing' chapter (K)
• check installation description (C)
• document new consecutive method (C)
• document 'What's new' (C)
• refer to modules (K)
• include more references (K)
• We could also think of finally including the gurobi solver option documentation (Gurobi SolverOptions documentation #213) in the rtd (K)