Update License.md md5sum on tools/check based on 2f4703e8

Add requirements.txt necessary to build and run validator

Make filter for id at definitions general

Adding url placeholder

The original plan was to put the URL for this repository in a configuration file that authors could edit when creating actual lessons.  However, it looks like Pandoc only does one level of variable expansion, so variables inside `_includes/footer.html` (which is itself interpolated as a variable) aren't expanded.  Instead, we will tell authors to edit `_includes/footer.html` in the `README.md` in the `gh-pages` branch.

Fix unittest for changes on motivation.md

This solves #77 by add id attribute to every item of a definition.

Add Unit Test target to Makefile

Test rework

Improve message for glossary error

Minor changes to make error messages consistent, and possibly less crashy. Still need unit tests to trigger this code.

fill in missing '$ ' in prompt

Improve callout box and "learning objectives" box

Add small script to setup label in lesson repo

Update validator for changes in directory structure

Updating files to move  into root directory

Add id to glossary entry

This is needed to enable users jump to glossary entries.

Merge of new validator with tests

Add validation methods and refactor ast helpers to separate class

Add tiny logging message; prep for first push to github fork

Start adding tests

Fix errors revealed by unit tests

Update validator to check heading order; tests passing

Validation of links and changes to heading validation

Tiny comment cleanup; push to share version with swc

Add some descriptive comments and create minimal validator example (for instructors.md) to demonstrate subclassing

Split helpers to separate file and update for newest index.md template

Grooming

Bring up to spec with newest versions of lesson templates. Add tests to ensure all templates pass validation.

Saner default assumption about markdown file locations

Add skeletons for remaining validators. Incorporate ranier's code for batch validation.

Code changes for single-file python 2 and 3 compatibility.

Refactor out template validation logic in prep for cmd line rework

Proof of concept refactor to command line sig for @rgaia-cs (issue #34)

With no path provided, default to curdir, not a hard-coded default

Implement license and discussion validators. Some test cleanup.

Validate file links against page titles. Add line length check.

Fix python3 hash error

Rename validator to check

Conflicts:
	tools/validate_markdown_template.py

Enforce section heading levels + pep8 cleanup

Improved link validation for non-html files

Validate images as well as links

Verify that all headings are exactly level 2

Link text validation based on document header "subtitle" instead of "title".

Adjustments based on run against the SQL repo.

Fix links to topics

By default only show erros and warnings to user

- Add another argument for CLI to enable debug log level
- Change some log message to debug instead of info
- Add file information for errors and warnings

Fix import at check

From [PEP8](https://www.python.org/dev/peps/pep-0008/#imports)

> Imports should usually be on separate lines, e.g.:
>
> Yes: import os
>      import sys
>
> No:  import sys, os

Heading bugfixes, update failing tests, and cleanup. fix swcarpentry/lesson-template#39, swcarpentry/lesson-template#42 .

Add validation of glossary

Slight clarification to log messages.

Skip validate some links in index

Fix super() call for python2; avoid mutable default argument.

Lesson template validator.

Splitting lesson instructions