DO NOT MERGE Docs revamp

[Mierdin]

TODO update docs with message about taking out:

    # If on Linux, enable ping testlet functionality (DEPRECATED in favor of granting socket capabilities on testlets)
    # sysctl -w net.ipv4.ping_group_range="0 0" || echo "Unable to set kernel parameters to allow ping. Some testlets may not work."

and instead going with capabilities modification. Need to create a doc that talks about testlet compatibility broadly (what about bsd? Windows?)

Also need to document the requirement that native testlets are in the PATH and provide some techniques through which this is achieved.

Also need to check on docs/customtestlets.rst, which was changed in the native testlets patch. Need to review this file in this path and ensure it follows the rest of the changes here. Also make sure docs/testlets.rst is looked at as well. Both of these files are separate outside of this PR

[Mierdin]

Not ready to merge yet. Relies on https://github.com/Mierdin/todd/pull/80