xcconfigs++
Merge pull request #938 from ReactiveCocoa/xcconfigs++

xcconfigs++
Update to jspahrsummers/objc-build-scripts@449d8fac8097dc236d6c9a46e353b9293249dc13
Stop `cd`ing around in cibuild, messes things up
Update to jspahrsummers/objc-build-scripts@006869577c9f5af9349ab2e4c3b6691199ec1e97
Merge pull request #942 from ReactiveCocoa/ci-lulz

Fix broken xcconfig references in CI
Added RACSignal+Operations.h as public.
Added umbrella header to mac static library target.
Added NSObject+RACKVOWrapper.h as public.
Stop some private headers from being exported.
Remove RACValueTransformer.
Merge pull request #946 from ReactiveCocoa/fix-header-visibility

Fix header visibility.
Merge pull request #947 from ReactiveCocoa/burn-racvaluetransformer

Remove RACValueTransformer.
Fixed -bufferWithTime:scheduler: not supporting nil values.
Added dedicated tests for NSNull and nil values in -bufferWithTime:scheduler:.
Merge pull request #948 from ReactiveCocoa/bufferwithtime-nil-values

-bufferWithTime:scheduler: nil values regression.
++xcconfigs for arm64 support
Merge remote-tracking branch 'origin/master' into 3.0-development
Merge branch '3.0-development' into subscriber-disposal