[JENKINS-37284] Added custom pipeline step

[cpoenisch]

Relates to issue #80 and JENKINS-37284.

Provides the ability to use a custom pipeline step without allocating a node and a separate build wrapper.

Instead of

node {
  wrap([$class: 'AnsiColorBuildWrapper', 'colorMapName': 'XTerm']) {
    <something that outputs ansi colored stuff>
  }
}

also following pipeline syntax can be used

ansiColor('xterm') {
  <something that outputs ansi colored stuff>
}

[dblock]

Looks good to me, @ejelly @qvicksilver also take a look pls?
Needs CHANGELOG and README updates, please.

[dblock]

Looks great, merging.

@cpoenisch Want to help out with the next release?

[lsglick]

Hi @dblock! Any idea when we'll see this in a new release? Thanks!

[dblock]

I was hoping someone else can do it, see #75. Add your +1.

[eyelock]

Also added my +1 to this, having the coloring in a non-node context would be pretty cool. Would love to do a release but pretty new to all this (teach a man to fish though ...)

[dblock]

I tried to make a release, but right now maven.jenkins-ci.org 8081 seems MIA :(

Will try later ...

[dblock]

OK, that host was discontinued, see https://twitter.com/jenkinsci/status/800526772773142530
I updated the pom.xml with the correct URL in 38ae5ec

[dblock]

This was finally released in 0.4.3. Thanks for your patience.