fix missing 'kind' arg in importer

fixes #983
Remove old mercurial files
Use the `docutils` variable to check if docutils is installed, not `core`.

+ remove duplicate import
Replace get_populated_generator with setUpClass
More refactoring for test_generators

- list comprehensions for distill_articles/pages
- distill articles only once
- pep8
Refactor pelican_open using contextmanager
Add warnings for img with empty alts. Fixes #647.

Unify Rst and Mkd: if alt is not specified at all, create an empty alt.
Warns the user in case of empty alts.
Move PDF generation to a plugin. Fixes #1009
Merge pull request #1003 from russkel/tumblrfix

fix missing 'kind' arg in tumblr importer
Merge pull request #1004 from russkel/hgrm

Remove old mercurial files
Merge pull request #1010 from kylewm/pdf-plugin

Move PDF generation to a plugin (Fixes #1009)
Merge pull request #895 from Rogdham/empty_alt

Add warnings for img with empty alts. Fixes #647.
Merge pull request #1006 from saimn/fix_docutils

Use the `docutils` variable to check if docutils is installed, not `core`
Remove the reference to the PDF generation in the docs. Fix #1013
Merge pull request #1007 from saimn/refactor-tests

Refactor test_generators and pelican_open
fix py3 support for sourcecode directive

added sourcecode to the functional test so it's tested *somewhere*.
fixes #963
Merge pull request #1002 from russkel/sourcecodefix

fix py3 support for sourcecode directive