Fixing readthedocs

[ipcamit]

The docs were not getting rendered as the read the docs file was not proper.

1. I modified the read the docs to correctly initialize the env
2. sphinx was overwriting the index.html to a blank one, and I could not find method to disable it. So conf.py now contains code to to copy the index.html and restore it.
3. On readthedocs, CMake was not generating the docs because of CMAKE_INSTALL_RELOC_DOCDIR variable not being initialized. So modified it to give a proper destination.

After these changes I can correctly generate the documentation on the fly: https://kim-api-docs.readthedocs.io/en/latest/

[ellio167]

Looks reasonable, I think.

However, the use of ${CMAKE_INSTALL_RELOC_DOCDIR} would be good to maintain. Perhaps, just use it to set the value of ${CMAKE_INSTALL_DOCDIR}, and revert to the original install line.

[ipcamit]

I tried restoring the original CMakeFile, and it works.