Convenience method to monitor custom transactions

Use Appsignal.monitor_transaction to instrument and log errors for
custom actions.
Add option to ignore a specific action
Remove ActiveSupport dependency and vendor notifications
Update cacert.pem
Merge pull request #132 from appsignal/cacerts_update

[WIP] Update cacert.pem
Merge pull request #138 from appsignal/no_dependencies

Remove ActiveSupport dependency and vendor notifications
Fix issue where backtrace can be nil
Merge pull request #141 from appsignal/fix_backtrace_cleaner

Fix issue where backtrace can be nil
Merge pull request #134 from appsignal/wrap_transaction

Convenience method to monitor custom transactions
Merge pull request #136 from appsignal/ignore_action

Add option to ignore a specific action
Update changelog for 0.10
Add example for ignore actions and fix spec
Bump to v0.10.beta.1 [ci skip]
Remove .
Use a Mutex in agent instead of Thread.exclusive
Merge branch 'master' into develop

Conflicts:
	CHANGELOG.md
	lib/appsignal/version.rb
Bump to v0.10.beta.2 [ci skip]
Bump to v0.10.0.beta.0 [ci skip]
Merge branch 'master' into develop
Merge branch 'master' into develop