Update symlinking for recursive submodules
Update link test suite for recursive submodules
More comments and a little refactor for get_repo_files()
Split test amendment by nitrobruno into two separate tests
Fix #115: Speed up the link command.

 - Don't store intermediate `paths` variable; use pipes.
 - Use process substitution to speed up loops.
 - Minor clean-up & fix a few shellcheck warnings.

1 test re: Fail on newline in filename does *NOT* pass.
Is this behavior we need to keep?
For #115: Update link file with newline test.

 - IFS manipulation did not appear to be doing anything helpful, so I
   removed it.
 - Linking files with a newline is not actually fixed, but the
   behavior did change slightly, so I updated the test.