Initial bits of the template tag
WIP commit of some tests and a bit more text
Couple more additions with a "left as an exercise"

Because who doesn't like "the solution for which is left as an exercise for the reader"
Reword intro, fix spacing and link, add a link
Improve explannation of file stricture
Improve inclusion tag section and incorrect rST
Add template tags page link to index
Fix first test and change post to entry
Fix description for zero and many posts tests
Add DRY URL as suggested by @willingc
Fix wording as suggested by @willingc
Fix code solution for blog_tags library
Add note about relative imports
Merge branch 'issue-10'