Release v0.3 of JPhyloRef

[gaurav]

This PR includes v0.3 of JPhyloRef, as deployed to Maven Central at https://search.maven.org/artifact/org.phyloref/jphyloref/0.3/jar. It includes some changes:

• Modifications to pom.xml to incorporate the nexus-staging-maven-plugin, which automates many of the steps in publishing a Java package to the Sonatype OSSRH.
• Publishing to Maven Central requires that Javadoc can be run on all source files. Unfortunately, our source files have e-mail addresses in a format that caused Javadoc to fail. This PR removes those e-mail addresses.
• Publishing to Maven Central requires some package metadata to be entered into the pom.xml file. This PR does that, and confirms that we meet all requirements to publish to Sonatype OSSRH. The code published to Maven Central as v0.3 have been tagged v0.3. Closes #50.
• I've also documented how to publish to Maven Central in the README file.
• Updates the CHANGELOG and tags release v0.3.

[gaurav]

@hlapp It was messing with Javadoc, since the format I used (e.g. Gaurav Vaidya <gaurav@ggvaidya.com>) was being misinterpreted as an invalid HTML tag. Since OSSRH requires that we generate Javadoc for JARs being uploaded, I had to fix it somehow. I considered replacing it with just the e-mail address or putting an <a> tag around it, but ultimately I decided that since my e-mail address was in the Git commits anyway, it probably wasn't necessary to put it into the source files as well. I can put them back in if you like, or add a CODEOWNERS file if you think that's a better idea.

[hlapp]

No worries. I was mainly curious.