refactor of release notes

* change form of release notes to make content easier to find
* add RC version history under 12.0
* minor accuracy/completeness updates to changelog.
Merge pull request #603 from opscode/mp/release-notes-sprucing

refactor of release notes, and minor accuracy/completeness updates to ch...
Provide a default value for LDAPS (port 636) when encryption is desired.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>