Tidying up after consolidating links

Rev 7da36a56 added a new row to the syllabus table with only 11 columns (instead of 12), which broke layout.
This fix adds the missing space.

Close #81

Close #80

Including mention of Library Carpentry in include files

Merge last changes on https://github.com/swcarpentry/styles/

Knit episodes only when any one RMarkdown source changes

Adding Google Analytics

add more information about pkgs needed to build the lesson

Unifying links in a single file

Adding comments on purposes of include files

Using page.previous and page.next for links instead of loop

lesson.scss: 2em left padding for lists

Auto-generating IDs for glossary items

Fixing layout of descriptions of standard pages

1.  Create file `_includes/links.md` with definitions of all links.
2.  Replace links at the bottom of Jekyll'd `.md` files with inclusion of that file.
3.  Modify `bin/lesson_check.py` to load and check definitions in this file.

This eliminates most redundancy in link definitions, though
`CONTRIBUTING.md` and `README.md` still contain their own links, since
they are not Jekyll'd.  Note that we *cannot* put the links into
`_layouts/*.html` (or even `_layouts/something.md`) because of the
order in which Jekyll expands things - we have to explicitly include
it in each page.

Change target of setup link from .md to site page

The link worked fine, but directing people to the setup.md file instead of the rendered page means that other links don't work - such as item 12 in the setup page: https://github.com/swcarpentry/lesson-example/blob/gh-pages/setup.md

Update a few files to make this directly readable on github