fixed type, then revised sentence for clarity

The typo was "easier to manag*ing* this distinction"

But while it was opened, I tried to make some text more concise, and explicit (e.g. converting "it" to "dev_mode()".

Please let me know if you would prefer that I stick to copy-edits rather than such revision.
Merge pull request #35 from dlebauer/patch-1

fixed typo, then revised sentence for clarity