Add a test of encoding multiple spatial layers

This increases the coverage of the unit tests.
Remove an unused gitignore entry

Nothing within this project will generate .ko files.
Merge pull request #533 from mstorsjo/remove-unused-gitignore-entry

Remove an unused gitignore entry
Merge pull request #522 from mstorsjo/layered-encoding-test

Add a test of encoding multiple spatial layers
Merge remote-tracking branch 'upstream/master' into travis.osx