[Documentation] Update HTML docs (#163)

With this patch, the following changes are made to the html docs.

* PR #153 is reflected.
* Explanation for the benchmarking tool in PR #98 is added.
* A small amount of explanation on the GNUABI version of library is added.
* Benchmark results are updated to comparison between sleef 3.2 and SVML comes with icc 18.0.1.