delete old files that have been replaced by a directory

Fixes #417.
Replaces #1086, more logical code.
test this fix with a cucumber feature
Add feature to test new functionality.
Remove superfluous "After" block from step defintions.
Fixed bugs with pagination in a subdirectory.
WIP – fixing tests.
Fix tests for Pager.
Add warning when pagination is enabled but no template page has been found
Fix Pager.in_hierarchy to actually do the right thing
Fix tests to match new behaviour of Pager.paginate_path
Edited the two contributing pages to ensure that they point readers towards site/docs for the docs rather than site/_posts (which doesn't exist)
Merge pull request #1214 from jadbirch/docs_correction

Very small documentation correction
Update history to reflect merge of #1214
removed cgi unescape in page destination
added a plus to permalink
Add ReadInXMinutes plugin
Merge pull request #1222 from zachleat/patch-1

Add ReadInXMinutes to plugin list
Update history to reflect merge of #1222
Remove plugins that have been obsoleted by changes in the core
Merge pull request #1223 from mojombo/remove-obsolete-plugins

Remove plugins that have been obsoleted by changes in the core