Add documentation around overriding `initWithDictionary:error:`

Fixes https://github.com/Mantle/Mantle/issues/336
++xcconfigs
Don't automatically build unit tests
Remove extraneous newline
Update example of pre-computed value from _titleLength to _retrievedAt
Update NSDate property to copy semantics
Remove unnecssary explanation about pre-computed properties
Fix indentation for consistency
Fix convention for checking self in -init
Merge pull request #365
Fix typo in README.
Merge pull request #376 from tomtaylor/master

Fix typo in README.
Merge branch 'master' into xcode6
++xcconfigs
Update to jspahrsummers/objc-build-scripts@a54782c
Purge static library targets, update Mac target
Recreate iOS target as a framework, misc settings
:fire: Specta and Expecta :fire:
Move xcconfigs to a new External folder
Add github/Quick