Fix installation paths and refactor

[sl1pkn07]

downstream bug: apache/mxnet#14692 (review)

• Added option to install documentation with -DINSTALL_DOCUMENTATION=ON (OFF by default)
• Refactored and remove duplicate code about headers & docs installation rules
• Install the headers and the docs following the GNU standard installation directories

[hcho3]

@larroy Can you review?

[larroy]

See my comment in your PR in mxnet. I think we are almost there, but there are errors when I try both PRs together.

[sl1pkn07]

thats seems is because needs update dmlc-core submodule into mxnet, pointed to updated dmlc-core with this pr applied

[larroy]

I did that, it failed. Could you submit a PR with the gitmodule directed to your repo so I can just clone and test?

[sl1pkn07]

i'm not sure if i do the things ok, but try: https://github.com/sl1pkn07/incubator-mxnet

[larroy]

thanks. Your TVM commit is too new, I checked out the same revision as in master: 0f053c82a747b4dcdf49570ec87c17e0067b7439 The newest TVM requires changes that are not yet merged to mxnet master.

[larroy]

This works. Let's get the prs merged. Thanks a lot!