Add NSPredicate query support to Cloudant Sync

This allows using an NSPredicate to generate the SQL for querying
over Cloudant Sync indexes, rather than using the dictionary
format. The dictionary format is left available, for those who
would rather use it.

The main NSPredicate to SQL processing happens in
CDTQueryBuilder, and CDTIndexManager has methods taking
NSPredicate objects added.
Merge pull request #57 from cloudant/NSPredicates-Support-For-Queries

Ns predicates support for queries
Remove deprecated APIs
Remove usage of deleted APIs from Sample

Remove the usage of deleted APIs from the sample app,
Also changed the description property to taskDescription to fix warning about property redeclaration (description is declared in NSObject)
Initial draft of api-migration doc
updates to api migration doc