Todo list for documentation

[shizejin]

• Create a new section called "Base Types and Methods" which includes NormalFormGame.
• Add random game to the section "Base Types and Methods".
• Change auto_doc_gen.jl, so that each section does not have subsections for files, but just has subsections of "Exported" and "Internal".
• Add a User Guide before Library.
• Add a description to docs/README.md about how to use auto_doc_gen.jl.

[oyamad]

• Modify the docstrings in accordance with the official documentation style, as in Doc style #25 (comment).

[oyamad]

• Revise the docstrings for the repeated game related functions; see the documentation.

[oyamad]

Remove the type declarations from the header. For example:

covariance_game{N}([rng::AbstractRNG], nums_actions::NTuple{N,Int}, 
                   rho::Real)

should be

covariance_game{N}([rng], nums_actions, rho)

or

covariance_game{N}([rng=GLOBAL_RNG], nums_actions, rho)

The type declarations are provided in the Arguments section.