Add documentation for bulk/batch operations

[imhoff]

Add support for multiple database interactions in one transaction. Implementing this will enhance performance while inserting a large amount of data into the database; and reduce the risk of getting a inconsistent database state if the application is closed during long running db operations (rollback).

[imhoff]

Two ways to implement this behavior are possible. By [using](http://developer.android.com/reference/android/content/ContentProvider.html#bulkInsert%28android.net.Uri, android.content.ContentValues[]%29) ContentProvider.bulkInsert(Uri uri, ContentValues[] values) multiple inserts into one table could be chained together. This would be just a minor adjustment to the current code as the basic implementation of bulkInsert is already provided by Android. The limitation of this method is that only inserts for one specific table are chainable.

The second and more complete option is using ContentProvider.applyBatch(ArrayList<ContentProviderOperation> operations)
This approach is neither limited to a single table nor to insert actions only. Unfortunately it is also a lot more complicated.

This question on Stackoverflow suggests using the second approach.

[fluxtah]

This is yettop be documented however Mechaniod can do this, see #121 for details

When I get a moment I will add to docs.

[imhoff]

Thanks man! Had a little look at the classes first but had no clue where to find it.