backport exception for invalid JSONKeyPathsByPropertyKey
only allow NSString or NSNull as JSONKeyPathsByPropertyKey value
no need to check if class is NSNull
some more fixes
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
Remove test that's invalid because of #349
++xcconfigs
Automatically select architectures
Update upgrade checks
Merge pull request #367 from Mantle/remove-broken-test

Remove test that's invalid because of #349
Merge pull request #368 from Mantle/zero-warnings

Zero warnings
Update README.md

Fixes #370
Update README.md
Merge branch 'master' into 2.0-development

Conflicts:
	Mantle/MTLJSONAdapter.m
	Mantle/NSValueTransformer+MTLPredefinedTransformerAdditions.m
	MantleTests/MTLJSONAdapterSpec.m