Remove temporary directory from sourcemap logging
Nest fixtures for manual testing

Moves them closer to our test data -- I want to test nested files with
sourcemaps. At some point we should make the tests either use the files in
fixtures or delete them and the gulpfile.
Give sourcemaps the correct paths to source

:boom:
Refactor tests a little

Consistent patterns and should be a good basic structure if we want to test more
than one file.