location_api: various bits of requested text clean-up

- Replace the "vary the world over" colloquialism with "vary
  widely around the world"
- "core DDG package" becomes "core DDG library"
- "Revelant" is a pretty sweet word.. but "relevant" is what
  was meant.
- Make link to API testing guide read less clumsily.
Merge pull request #42 from mwmiller/more_location

location_api: various bits of requested text clean-up