Implement usage of SemVer ordering rules for resolving previous artifact

[UnasZole]

As title says, makes it so that resolving the previous artifact follows the ordering rules defined in SemVer 2.0.0 specification ( http://semver.org/spec/v2.0.0.html ).

Not complete yet : I'm planning to add some JUnits on the JApiCmpMojo to validate the changes better, and probably to improve management of error cases.
Still, I wanted to open the PR to get feedback on the principle before finalising everything :-)

Basically :

• Extends SemanticVersion class with ability to parse according to the spec, and implement Comparable following the spec's rules.
• Create SemanticArtifactVersion implementing Maven's ArtifactVersion interface.
• Do some crazy stuff to get these SemanticArtifactVersion inside the maven version range used for comparison.
• Add a plugin parameter (false by default) to enable this behaviour.

Also, one point to note : I added dependency in test scope to hamcrest matchers in order for my JUnit to use assertThat cleanly, being consistent with your JUnits.
If you are unhappy with the dependency addition, I could rewrite the tests to use good old assertTrue, it's not a big deal :-)

[siom79]

Thank you for providing a pull request. Your implementation looks fine. I would merge the PR once it is finished. Please also extend the documentation under src/site/markdown.

[UnasZole]

Thanks for the feedback, and sorry for the late answer :-)
I'll do that as soon as I get a bit of time.

[twogee]

@UnasZole may I help you to complete the PR?