Sphinx documentation improvements

[tkeskita]

Hi,

here's a first suggestion to remove generated Sphinx docs from source tree: Keeping them in source requires manual building when changing docs, and the results differ depending on Sphinx version and environment, resulting in many commit changes. It also increases repository size. I assume docs are anyways automatically built upon commit on readthedocs site? It's easy for users to read docs on-line or build docs themselves locally if needed.

Also added :noindex: entries to rst files to avoid Sphinx warnings about duplicate object descriptions.

PS. I'm now trying out a pull request workflow described in https://github.com/CoolProp/CoolProp/wiki/Contributing:-git-development-workflow which should be maintainer friendly!

[tkeskita]

Updated with suggestions for changes in Sphinx docs

[gustavochm]

Thank you so much for time and efforts!!