Added 'present' property.
Removed 'eventually' in favor of compatibility with chai-as-promised, plus the functionality is not strictly webdriver-related.

Also reformatted to 4 spaces. 😱
Minor test correction. (still fails, though, but for the proper reason)
Unwrapped `#visible` promise, seems to cause test issues.
Removed `eventually` from readme, bump version to 5.2.1 (didn't want to blow through to v6 just yet.)