Small fixes and cleanup

[jessebraham]

Nothing too interesting here:

• Don't depend directly on strum_macros, as it is already pulled in by strum's derive feature
• Use the directories package instead of using both dirs and directories-next
  • Ironically, directories is now more up-to-date than directories-next
• Fix some small typos in the output, use more consistent quoting
• Silence the output from invoked script/application when installing Rust
  • This looked out of place in the output; there may be other places where this should be done as well
  • Might be a good idea to pull in the indicatif package and have status spinners for each step in the future?

[SergioGasquez]

LGTM! Thanks for improving espup so much!