minor spelling, grammar, formatting fixes

Lots of minor fixes sprinkled throughout the files:

M-file docstrings
rk_opt.m     - Python >>> to MATLAB >>
am_radius.m  - RST LaTeX formatting of equations
rk_stabfun.m - RST LaTeX formmating of equations

RST-file documentation
index.rst    - RST formatting for description list
               pacakge spelling fix
future.rst   - Better GitHub links
started.rst  - RST formatting ` ` to `` ``
               Path changes to make addpath call clearer
               Python >>> to MATLAB >>

Updates to generated files
RK-coeff-opt.rst - see changes to .m files
RKtools.rst      - see changes to .m files