Write program to deep merge JSON documents.

git-svn-id: https://source.caret.cam.ac.uk/svn/projects/timetables/trunk/app/scripts/stats@21706 59899196-baf2-4bc4-a94d-4a08719e171f
Move assertion in jsonmerge, was asserting the wrong thing!

git-svn-id: https://source.caret.cam.ac.uk/svn/projects/timetables/trunk/app/scripts/stats@21928 59899196-baf2-4bc4-a94d-4a08719e171f
Fix json_merge_all() behaviour on empty list

When called with an empty list, json_merge_all() would return the
MISSING marker object. It now raises a ValueError indicating that the
input sequence was (incorrectly) empty.
Add unit tests for jsonmerge
Add LICENSE file
Add README.rst