There is currently no way to create a multi line description based on multiple regex. The "Flexible publish" plugin gives me the possibility to call the description-setter plugin multiple times, but the last description-setter overwrites the result of the one before.

Therefore I added two checkboxes in the job configuration page for the plugin: One that says "Append description to existing description", which then calls build.getDescription() and prepends it to the current description.
The second checkbox "Append in a new line" is self explanatory and adds a "<br />" between the existing description and the current description.

I've also added the helppages, but I'm not sure if this is the right way to specify a help file for an optionalBlock element:
<f:optionalBlock ... help="${descriptor.getDescriptorFullUrl()}/help/setAppend">

but it actually works.

I would appreciate if you would merge my branch, because I think other people would need that feature as well.