Update change log

Update pod spec

Merge pull request #88 from Sigmapoint/message-visible

Changed property to 'readonly' from outside

Moved 'messageVisible' flag to .h file so that it can be read from outside

Updated version, pod spec, change log

Fixes #67

Merge pull request #83 from rexeisen/master

More fixes for #64

Fixed #64

Merge pull request #86 from Zeeker/bugfix/callback-messages

TWMessageBarManager: Fix a bug where messages which were presented from the callback of a message wouldn't show up

- Added nullability annotations to better support Swift projects.

Updated changelog, podspec and readme

Fixed for orientations via #59