Update release and publish process

[dr0i]

#306 comes up with some quirks which should be adressed:

• @cboehme is noted as the releaser. [edit] fixed by setting the travis variable GITHUB_RELEASE_TOKEN to my own
• the release is published to nexus sonatype [edit] but there is a problem with travis and sonatype, see the gradle-nexus-staging bug. Got problems with that new plugin, too. For now, as a workaround, it's deployed from my local computer, which works, but the configs are not yet commited and must rethink of how to handle pgp keys. [edit] Described the new way of doing a release in the wiki.
• the release is not published to maven repositories [edit: it's published to the Central Repository which is good enough(and may be synced to mvnrepository.com some time in the future, don't know)
• would be also nice to note new maintainers @fsteeg and @dr0i in the pom.xml rmove developers section from build.gradle

[dr0i]

Updated the Maintainer-Guideline.

[dr0i]

Updated the Maintainer-Guideline again, reflecting the new way of doing a release.