Update README to include instructions for use with Immutant.

This is as recommended by Toby Crawley (@tobias) in #80.
[Fix #88 again] Set up DTD for HTML parser.

Invoking the HTML parser explicitly worked around one reference to
`AppContext`; however, to work around another, we need to set up the DTD
explicitly we well.
Use consistent return type (URL) for file/resources.

Accompanies `cider` #663.
[Fix #10] Add apropos middleware.
Add tests for apropos middleware.

Also, update some comments.
Add apropos middleware to README.
Ensure correct line number for tests on error.

The default `:line` event property conveys the line where the exception
was thrown. Traverse the stack to get the line number for the test source.

Fixes CIDER #648.
Fix typo.
Merge branch 'master' into cljx-info
Remove cljx dependency on Clojure 1.6, use io/input-stream, add test