Fix inherited queries when accessing cursor by index

Now the document class will be set correctly in code like this::

    doc = cursor[3]
Updated unit test
Merge pull request #148 from asivokon/master

Inherited queries are now supported when accessing cursor by index
changed the namespace on schema document errors
Merge pull request #153 from rtjoseph11/master

changed the namespace on schema document errors
fixing typos within README.md
Merge pull request #158 from 1123/master

fixing typos within README.md
fix test where to_json method is compare to a string

as in pyhton and json the order of the keys is not garantee,
we cannot compare to_json output directly with a hardcoded string.
I'ts better to transform both the hardcoded dtring and the to_json
output in json with the json library and compare the 2 resulting objects
Merge pull request #160 from mobyle2/fix_to_json_unit_test

fix test where to_json method is compare to a string