Issue #1107522 by MegaChriz, twistor, ditcheva, nielsonm, franz, Niklas Fiekas, cthiebault, Uhkis, gcb, mparker17, guillaumev: Framework for expected behavior when importing empty/blank values + text field fix

Issue #2333029 by twistor, MegaChriz: Extend mapping API to allow for defaults and multiple callbacks

Issue #661606 by MegaChriz, twistor, Cottser, scottrigby, manojbisht_drupal, Mohammed J. Razem, agileadam, emilyf, tmsimont, bradjones1, hairqles, ldavisrobeson, selim13, a.ross, chromix, g089h515r806 | lunk_rat: Added Support unique targets in mappers.

Issue #1080386 by elizzle, twistor, rhouse, AndyF, chadmkidner, retiredpro, slefevre1, moonray, asgorobets, jwmeyerson: Added How to get title and alt fields into your image import for drupal 7 feeds.

mapper: URLs with spaces not parsed properly.