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 04:08:54PM -0800, Greg Wilson wrote:
> I'm the maintainer for now - I'll ask for a volunteer to take it
> over in January.

Then I have no problem with you just merging things like this
yourself.  Hitting the big green button or running the merge locally
is probably faster than asking someone else to do it ;).