backport exception for invalid JSONKeyPathsByPropertyKey
only allow NSString or NSNull as JSONKeyPathsByPropertyKey value
no need to check if class is NSNull
Ordered relationship deserialization to NSOrderedSet vs NSMutableArray
some more fixes
Merge pull request #352 from rawrjustin/nsorderedset-deserialization

Ordered relationship deserialization to NSOrderedSet vs NSMutableArray
Add Slack chat room to README
Linking to a PR within the PR

So meta.
Merge pull request #357 from Mantle/jspahrsummers-patch-1

Add Slack chat room to README
Revert "Merge pull request #352 from rawrjustin/nsorderedset-deserialization"

This reverts commit b1d3eac764e9eae8830cd2cf6c2622f7194b3eda, reversing
changes made to c6a4f0b06ca6c46f0275abaa86973e3f96faa8ef.
fix grammar in error message
Merge pull request #363 from 5teev/master

fix grammar in error message
Move to specta/specta, specta/expecta, and XCTest
Merge pull request #364 from Mantle/xctest

Move to specta/specta, specta/expecta, and XCTest
remove last usage of _JSONKeyPathsByPropertyKey
Merge pull request #349 from Ahti/invalid-json-keypaths-exception

backport exception for invalid JSONKeyPathsByPropertyKey
Add documentation around overriding `initWithDictionary:error:`

Fixes https://github.com/Mantle/Mantle/issues/336
Remove test that's invalid because of #349
++xcconfigs
Automatically select architectures