Minor changes.

* Modify README.md.
* Rename LICENCE -> LICENSE.
* Fix typo.
Unit-test for the JSON implementation.

First test-suite to test the functionality of the JSON implementation.

It is written with the Boost.Test framework which feels pretty sweet to
write & execute brief test cases. To build and run all unit-test, simply
execute following command:

b2 tests -q

This is a first step to fix issue #1. More unit-tests coming soon.
Better exception handling in query_collection.