Merge branch 'release/v0.20.0-rc1'
Merge branch 'release/0.20.0'
Drop pre from README.md install instructions
Merge branch 'release/0.20.1'
Adjust version and tag in Podspec for release
Merge branch 'release/0.20.2'
Merge branch 'release/0.20.3'
Merge branch 'release/0.21.0'
Merge branch 'release/0.22.0'
Enable `GCC_WARN_64_TO_32_BIT_CONVERSION` warning
Respect `assignsDefaultValueForMissingAttributes` when mapping `nil` values

* Set `assignsDefaultValueForMissingAttributes` to `YES` for request mappings to enable serialization to NSNull
Merge branch 'hotfix/fix-nil-assignment-bug' into development