docs: Updated README.rst

* Added build status image.
* Added pip install command for generating docs
* Rewrote testing section to reflect new mock tests

Joe MacMahon <joe.macmahon@cern.ch>
tests: Wrote tests for previously not-covered code.

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
tests: Fixed testfixtures error.

* Running ./run_tests.sh no longer runs testfixtures.tests

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
tests: Removed testfixtures code.

* Testfixtures log capture didn't work well with threads for some reason.
  Replaced with own Handler class.

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
actions: Used a class instance variable to hold the logger.

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
tests: Updated test for build_mapping.

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
general: Replaced .copy() with deepcopy()

* This fixes a failing test (SchemaTestCase.test_update_mappings)

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>
tests: Added PEP8 checks as part of testing.

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>