Ticket History #7455: Documentation: table formating and ref correction in MIT features

Few issues:
1. Do not tie KFW 4.0 to 1.11 release.
2. Improve Quick facts table structure with regard to the following
cells: Platforms, PRNG and pre-auth mechanisms
3. Clarify reference to GS2

Update feature list in the documentation

In Quick facts section:
- restructure the Supported platforms section;
- do not tie KfW to 1.11 release;
- move references to GSS-API extensions to Feature list table.
In Feature list section:
- reformat the table;
- move PRNG and Pre-auth mechanisms into their own tables;
- clarify GS2 feature description;
- reference rfc6680 for GSS-API naming extensions.
Lowercase the words in the title of the document.

(cherry picked from commit 433329ec97598c14f8b64af3e6be7745501b7142)

https://github.com/krb5/krb5/commit/62e5ae9327df39803524ba187c43157dab6a87d9
Author: Zhanna Tsitkov <tsitkova@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 62e5ae9327df39803524ba187c43157dab6a87d9
Branch: krb5-1.11
doc/mitK5features.rst | 160 +++++++++++++++++++++++++-----------------------
1 files changed, 83 insertions(+), 77 deletions(-)