Revived prefixes from #40

In #40, we were making progress on prefixing everything to avoid conflicts. In this PR:

- Continue working on top of #40 
- Prefixed all externally exposed functions/variables to use prefix
- Fixes #39 

I have finished the version with `prompt_` in 137a5c0 but am going to update this PR to use `sexy_bash_prompt`.

/cc @luizfb @rpdelaney