Point gemspec to gem's real home, its GitHub repo

* And use Tobi's @mesosphere.io email address
Use API v2 for listing apps
Use v2 API for starting apps
Use v2 API to kill (DELETE) apps
Use v2 API for listing tasks and connect to CLI
Hook task killing up to the v2 API, add to CLI
Point 'scale' at the v2 API

The current state is fetched before PUTing the updated version of the
app. PUT replaces the current state of the app, which means it must
GET the current state to prevent unwanted changes to the state.
Rename "stop" command to "kill" to communicate effect

"stop" doesn't properly represent the destructive action that it does.
"kill" is the same term used in Unix for halting processes, and it
properly communicates that the app will not be recoverable.
Point "endpoints" to v2 /tasks with text/plain MIME type

* Also add support to the CLI for the "endpoints" command
Require an ID when creating an app
Add defaults for instances, CPUs, and memory
Remove 'default' note from scale, instances is required
Merge pull request #10 from mesosphere/v2-api

Use Marathon's V2 API