Merge pull request #77 from wlixcc/master

1.  Update to swift 5

Update Beethoven.podspec

Update Beethoven.podspec

Merge pull request #49 from vadymmarkov/swift4

Swift4 migration

Update Beethoven.podspec

Merge pull request #40 from vadymmarkov/refactor/transform-strategy

Refactor/transform strategy

Update Beethoven.podspec

Merge pull request #33 from vadymmarkov/fix/input-signal-tracker

Make audio engine optional

Update Beethoven.podspec

Add private Cartfile for tests