Update to release 0.8.1

Merge branch 'develop'

Update SPM for Swift 4. Update Tests for SPM

Update .swift-version

Set .swift-version to 3.2

Update podspec with prerelease version 0.7.0-alpha.1+swift4

Bump version to 0.6.9. Update Changelog.

Bump version to 0.6.8

Release 0.6.7 - for Xcode 8.2

Bump 0.6.6. Update CHANGELOG.