Upgrade to CC BY 4.0

Address  #8.

## Step by Step

~~~
$ cd lesson-template
$ git format-patch -1 --stdout 7d018cca > /tmp/cc.patch
~~~

Edit `/tmp/cc.patch` to remove conflict due "Software Carpentry, Ltd" vs "Software Carpentry Foundation".

~~~
$ cd ../workshop-template
$ git am /tmp/cc.patch
~~~

Edit `LICENSE.md` to back changes due previous conflict.

~~~
$ git commit -a --amend
~~~

@wking Could you check that the commit is OK?
On Sat, Dec 20, 2014 at 09:51:51AM -0800, Greg Wilson wrote:
> If you're sure the text is correct, please merge.

Are there maintainers for this repository?  I don't see one listed in
the old bc notes [1].  We should probably get someone who's officially
in charge to take responsibility for vetting and merging pull
requests.  I don't think I've been paying enough attention to this
repository for that person to be me, but now that the novice history
extraction is wrapping up I have more SWC time available…

[1]: https://github.com/swcarpentry/bc/blob/gh-pages/CONTRIBUTING.md#topic-maintainers