marked "freelink with spacelink" test as TiddlySpace-specific

moving it to a more appropriate module in the process

/cc @cdent
fixed vertical whitespace

for PEP8 compliance
renamed variable to indicate its a global

PEP8 says such constants are to be "written in all capital letters"

/cc @cdent
added link to source repo
added option for custom extensions
Merge pull request #19 from tiddlyweb/extra-extensions

added option for custom extensions
release 1.1.0

* adds support for including extensions through configuration
  (see for example: https://github.com/FND/markdown-checklist )
Merge branch 'master' into abstract-interlinking

Conflicts:
	test/test_freelinks.py
	test/test_spacelinks.py

Apparently my master was not up to date when I branched. feh.