#104 Support multiple launchers (entry points)

[donmendelson]

Plugin configuration changed to support multiple instances of launcher. Also, field mainClass is added to the launcher.

Example:

<launchers>
	<launcher>
		<name>xmldiff</name>
		<module>diff.merge</module>
		<mainClass>io.fixprotocol.xml.XmlDiff</mainClass>
	</launcher>
	<launcher>
		<name>xmlmerge</name>
		<module>diff.merge</module>
		<mainClass>io.fixprotocol.xml.XmlMerge</mainClass>
	</launcher>
</launchers>

This configuration adds these parameters to the jlink command line:
--launcher xmldiff=diff.merge/io.fixprotocol.xml.XmlDiff --launcher xmlmerge=diff.merge/io.fixprotocol.xml.XmlMerge

[gunnarmorling]

@donmendelson, thanks a lot. Feeling really bad about ignoring this for so long :(

Good change overall, one question only: will the previous single launcher configuration still be working?