Remove applicationId from library project

Specifying applicationId in library project is meaningless.
As of 1.0.0-rc1, setting applicationId in library project causes build failure.
see http://tools.android.com/tech-docs/new-build-system
Fix typo (buckoff -> backoff)
Ensure grabbing 'Application' Context to avoid resource leak
Avoid unnecessary hashtable search
Throws IllegalStateException when multiple PureeOutputs are registered for single type.
Merge pull request #12 from zaki50/remove_applicationId_from_library_project

Remove applicationId from library project
Merge pull request #13 from zaki50/fix_typo_backoff

Fix typo (buckoff -> backoff)
Merge pull request #14 from zaki50/ensure_application_context

Ensure grabbing 'Application' Context to avoid resource leak
Merge pull request #15 from zaki50/avoid_unnecessary_hashtable_search

Avoid unnecessary hashtable search
Merge pull request #16 from zaki50/prohibit_multiple_PureeOutput_registration_for_single_type

Throws IllegalStateException when multiple PureeOutputs are registered for single type.
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Update README.md
Use return value of last filter when multiple filters are registered.

problem 1.
  filter's return value null is ignored if one of following filters returns non-null value;

problem 2.
  if filter returns new object instead of 'jsonLog' argument and following filter exists,
  the returned value is overwritten by value from following filters.