Add support for NSValueTransformers in SDDataMap.

The `sdmo_transformed_key` macro is now available for use in data maps. It
accepts the same argument as `sdmo_key` along with an additional argument to
indicate the name of the value transformer that should be used. Using a value
transformer will preempt any cascaded mapping that might happen based on the
property type, including coercions from null. The value transformer is fully
responsible for any data conversions of the source data into destination data.

Example uses of this can be to use a value transformer that converts from
string descriptions to an enum, or to convert string URLS in NSURL instances,
or simply to invert a boolean value to match how the model prefers to store a
flag (e.g. service sends visible: YES but model wants hidden: NO).
Use `transformerClassName` to make intent clear.
Merge pull request #137 from walmartlabs-samsclub/feature/data-map-transformers

Add support for NSValueTransformers in SDDataMap.
Merge pull request #139 from walmartlabs-asdaios/master

Changes from ASDA fork - 3.0/3.1
SAV-504 this fixes a side effect that was introduced in my original SAV-504 fix.  It also fixes AIOS-1394
Merge pull request #140 from walmartlabs-wmusiphone/issue/AIOS-1394

SAV-504 this fixes a side effect that was introduced in my original SAV-...
Merge branch 'master' of https://github.com/setdirection/ios-shared

# By Jason Foreman (2) and Spencer Miles (1)
# Via Brandon Sneed (2) and others
* 'master' of https://github.com/setdirection/ios-shared:
  SAV-504 this fixes a side effect that was introduced in my original SAV-504 fix.  It also fixes AIOS-1394
  Use `transformerClassName` to make intent clear.
  Add support for NSValueTransformers in SDDataMap.