Implementation of Greg Wilson's template

This is up for discussion, but at the moment is the
minimal set of files needed to be a Software Carpentry lesson.
Ensure that checks are run from repo root
Initial version of shared files
Merge branch 'master' of https://github.com/tbekolay/swc-shared into gh-pages

* 'master' of https://github.com/tbekolay/swc-shared:
  Initial version of shared files

Merging to get `tools/update` so that this pull is automated
Using template variables everywhere
Merge pull request #1 from gvwilson/gh-pages

Using template variables everywhere

- Fixed error in header.html; missing }
LICENSE.md: Bump the CC BY 3.0 to 4.0

Titles from the v4 release notes [1]:

* A more global license
* Rights outside the scope of copyright
* Common-sense attribution
* Enabling more anonymity, when desired
* 30-day window to correct license violations
* Increased readability
* Clarity about adaptations

[1]: https://creativecommons.org/version4
Merge pull request #3 from wking/cc-by-4.0

LICENSE.md: Bump the CC BY 3.0 to 4.0
Initial commit
Merge branch 'gh-pages' of github.com:tbekolay/swc-template into gh-pages
Importing material created by @tbekolay in a personal repository
Ignoring more files
Adding a note to remind authors to say what learners are supposed to do in lessons
Merge pull request #2 from gvwilson/gh-pages

Adding a note to remind authors to say what learners are supposed to do in lessons.
Reorganizing material to put page source in sub-directory:

* Add `.nojekyll` to stop GitHub trying to compile.
* Get rid of Jekyll `_config.yml`.
* Create placeholder `css` and `img` directories.
* Create `pages` directory with source for web pages.
* Move all Markdown files into `pages`.
* Move `tools` into `pages` (because that's where people will mostly work).
* Move `_includes` and `_layouts` into `pages` (because that's where we'll compile).
Rationalizing tools.

1. Moving all commands into a Makefile (because we're handling file dependencies, and that's the right tool for it).
2. Ignoring the .html files produced in the root directory for now.
3. Switching to a single layout modeled on that used for workshop websites - will need to update this.
Bringing in description of lesson structure
Including things in templates
Example of including image in file
Another editing pass on the explanation for the template