Add hyperbolic tangent valve

[menon-karthik]

Closes #76

Added a hyperbolic tangent valve as described in #76.

I also made some other changes along the way:

• Updated the docs in a few places. The main updates were to remove the Wiki page in README, add a few more references, and fix the documentation in BlockType, BlockFactory, ClosedLoopCoronaryRight and SimulationParameters (which weren't getting built by Doxygen before).
• I moved InputParameters from BlockType to Parameters
• Renamed some variables in SimulationParameters to make it more readable
• Uncommented some debug messages (which I actually used while debugging) since they are executed only in the debug build and they don't need to be commented.

[mrp089]

And nice work, @kharold23! Feel free to reply to the comments as well (if you want).

[mrp089]

Splendid!