Updated documentation to include `autodoxygenindex`

With this in place, it documents the entire file as opposed
to just the class done in the previous commit.
Further onwards a small script to add `.rst` corresponding
to `.h` files should suffice in generating documentation.
Updating comments for .h files

Updated the conf.py tp add breathe_source_projects
Added .rst corresponding to .h files
Untracked csympy_config.h file.
Updated rst to use doxygenfile instead of autodoxygenindex

Using `doxygenfile` directive instead of `autodoxygenindex`
This generates valid documentation as opposed to previous  case.
[WIP] Documenting source files

Documented
* add.h
* basic.h
* functions.h
* integer.h
* symbol.h
[WIP] Contd: Documenting source files

Documented
* monomials.h
* mul.h
* ntheory.h
* number.h
Updated documentation for remaining files

Updated documentation for
* dict.h
* mul.h
* pow.h
* rational.h
* rings.h

There is a minor issue with `breathe` not generating documentation
for only functions defined under namespace.
Rest this is good to be merged.
Merge pull request #122 from sushant-hiray/documentation

Update documentation formatting