Ripping out external dependencies.

We now depend on ruby-hmac and addressable, and their days may be numbered.

We're doing this because:

  1. rails depends on a rack version that is minor higher, but same major (supposedly compatible if they're following SEMVER)
  2. rails depends on an activesupport version that is major higher, and thus uncompatible
  3. activesupport 4 is 1.9+ only, but we need to be 1.8.6, 1.9.3, and 2.0.0

So our first solution was to remove version dependency, but that's not good open source behavior (point to @ewdurbin!).

Next we thought about switching to a new library, but none of them seemed to be able to produce the same signatures (usually because they do too much).

Now we've decided the best choice was to just move over the functionality to our side and maintain it ourselves for now. This removes two hard annoying dependency (activesupport and rack).

In addition I've gone ahead and made this gem more modern:

  - No need for sample ruby-version/gemset files as they don't actually do anything (rvmrc stays the same, because random bash)
  - Using normal requires in the core file
  - Moving external dependencies to core file
  -