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.
    fix bug that there is no output in encoder console
Merge pull request #534 from ruil2/encoder_ret

    fix bug that there is no output in encoder console
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