added documentation (work-in-progress)
Added documentation to billing files.
Merge branch 'master' into docs

* master:
  Update changelog.md
  Ignoring uneeded files
  Added the option to overwrite an object in StoreInfo and save it

Conflicts:
	SoomlaAndroidStore/src/com/soomla/store/data/StoreInfo.java
Added documentation
Added documentation
fixed documentation
Fixed (my) mistake in KeyValDatabase
Added documentation
Changed documentation
configuration files