Adding slugify to the requirements.txt
Add slugify dep to README.md

Closes #15
Setting mode bits to better identify executables

Adding a+x to bandcamp-dl.py so it's identified as the main executable
Removing a-x to bandcamp-dl.py so it's recognized as a dep

Relates to #15
Merge pull request #16 from josefnpat/patch-1

Adding slugify deps to docs and changing mode bits