Fix JENKINS-18014

Changed the way that macros are escaped to using something similar to Groovy with two $'s. This required actually looking for the items that matched with two $'s and then handling that case special.
Merge branch 'master' of https://github.com/jenkinsci/token-macro-plugin
Fixed test for backslash
Merge pull request #12 from slide/master

Fix JENKINS-18014