Avoids leak warnings. Fixes issue #4.
Merge pull request #5 from hwaxxer/master

Supress warnings on `-performSelector:` (issue #5)
Add new utility macros from https://github.com/jspahrsummers/libextobjc
Add predefined transformation blocks for mapping methods
New block type names, some comments fixed
Add macro for observing single property, since this is the most used case
Merge branch 'master' into 'develop'
Consolidated comments from previous merge
Foreign observation block refactored, now have weak self parameter
Fix possible mutable key-path by copying it
Create first tests
Updated README and LICENSE
Merge branch 'release/v2.1' into develop