Update README.md
Merge pull request #57 from andrewtat/master

Update README.md
Fix typo in README.
[#ANDROID-178] ConcurrentModificationException in survey code.
Refactor database accessor method to remove it from Apptentive.java, and turn it into a singleton so it doesn't get recreated on each access. Since I was synchronizing on the instance, this was probably the source of some database locking problems.
Use finally/close pattern for closing cursors and db connections in database code. Fix dev test activity to actually delete messages when the Delete All Messages button is pressed. Remove some warnings.