Asynchronous task support for entry and render()

Moves the logging logic into the render() method, and then wraps up the
existing entry point code and the render() method to support an ES6
Promise-based control flow.
Rewrite render() to support asynchronous returns

The render() method will now be able to accept promises back from the
methods to retrieve the data object and to retrieve the template
rendering function.
_getData methods now asynchronous

This mainly rewrites the main _getData() method to return a promise
resolve or reject it through that interface, but also changes the
existing _getDataFromFile to throw an error rather than writing out to
the console if the file is not of an acceptable format.
Introduce intermediate _getRenderFn() method

This new method will serve as a go-between just like _getData()
currently does, and will provide validation and routing for the template
lookup.
Only display stack trace with --verbose

These are quite lengthy and do not serve a purpose unless you are
debugging the plug-in code itself.
Check for empty strings

Verifies that neither template nor data is given as an empty string.
Implement remote template URLs

This also brings in a new module: request.
Remote data support

This adds the js-yaml package, which is the same one used by Grunt for
loading YAML data natively from the file system.
Update documentation for remote URLs

Template and data can now be URLs or paths. Updated examples.
Add unit tests for URL versions of JSON/YAML/YML

These work by grabbing repository files from raw.githubusercontent.com,
so they ought to produce the same results as the local file system
versions.
Display fetch messages to console log

This helps clue the user as to what's going on if the remote server is
being a little slow.
Display problem URL with any download exception

This assigns a 'url' property onto the exception before it is rejected
and passed up the chain.
Remove Node.js 0.9 from test suite

This version is no longer available to the test suite.
Merge pull request #18 from corpulentcoffee/async-with-urls

Allow asynchronous downloading of data and templates over HTTP or HTTPS