Migrate from Command to inputTask.

1. You don't need to delegate to super.globalSettings (or any of those) if you provide
   settings in your implementation.
    The default *are* (and will always be) empty.

2. InputTask should be prefered to Command because it interacts better with other
   aspects of sbt, including being re-usable in other input tasks and having
   simpler API.

3.  I use the .? and the .value mecahnism of sbt DSL.  The first is to allow
    for a setting not to exist and not fail the build if the plugin is added,
    the second is how you grab a setting's value when you're in the task/setting
    system (vs. the underlying hardcore API).

4. Use the provided `streams` key for every task rather than logging to State.log,
   which is reserved for things which are unable to access any other logger,
   like Commands + boot startup, etc.  Also, wired an sbt.Logger through
   the methods.

5. Swap from using globalSettings to projectSettings.  BOTH would work,
   and global settings may be a better option in general, except for
   the autocompletion *NOT* handling input tasks on global settings right
   now :(.

6. Swap to use autoImport rather than Import (which I didn't realize worked).

Otherwise  a NICE example plugin.  Code was super clean.  Hope this shifts help.
Merge pull request #1 from jsuereth/master

Migrate from Command to inputTask.