[infrastructure] Upgraded HAML
[infrastructure] Supplied ~> versions for all libraries
[infrastructure] Eliminate clash between latest GLI and Rake

requiring in rake was causing some sort of conflict with GLI. Was not
necessary until later on in flow, so moved down.

Previous error message was:

  private method `desc' called for main:Object

And this impacts earlier versions of reveal-ck that brought in GLI 2.7
with a fresh bundle.
[infrastructure] Updated to latest of all gems

Removed Gemfile.lock and all version dependencies in the .gemspec and
did a "free bundle." Then, went back, and supplied '~> x.y.z' for all
resolved values.

Intention: get the latest and greatest, see that it passes specs, and
keep rolling.
[markdown] Provided support for :markdown blocks within haml