Test organization

Create 'AddCatchallTest' parent class for test cases. Re-organize all
'add_catchall' tests.
'add_catchall' targeting tests

Add tests for 'target_request_method' and 'target_view_kwargs'
parameters of the 'add_catchall' function.
'add_catchall' targeting

Implement 'target_view_kwargs', 'target_request_method' parameters for
'add_catchall' function. These parameters allow the user to specify
rules restricting which views the catchall endpoint will be applied
to.
Merge branch 'dev/catchall-targeting' into develop
Prepare release 0.3.2

Update version number.

Update changelog.

Clean up tests.
Merge branch 'release-0.3.2'