Revert "Use a Mutex in agent instead of Thread.exclusive"

This reverts commit 2ece482ece5cbaaeeadc572c431de4cec7e6fed6.
Remove Thread.kill duplication
Bump to v0.9.5 [ci skip]
Convert transaction to primitives when sending through pipe
Only convert to primitives and truncate once
Bump to v0.9.5 [ci skip]
Merge branch 'master' into develop

Conflicts:
	CHANGELOG.md
	lib/appsignal/version.rb