Support for existing meta lines in source plugin.yml, and new meta entries

[nklyshko]

Changes:

• added support for existing meta lines in source plugin.yml
• added support for api-version meta item
• removed rewrite of source file, because editing user's source code without backup is not good thing

Checklist:

• Have you read text of project license?
• Have you described maked changes in README or wiki?
• Have you added changelog?

[nklyshko]

Unfortunately, my tries to manual test changes locally was failed because i was unable to publish this plugin to maven local. If you can explain how to do this properly, I will check my changes in work.

[osipxd]

Thanks for your contribution!
Everything looks good except one small comment.

Now about your question:

my tries to manual test changes locally was failed because i was unable to publish this plugin to maven local

At this moment plugin in develop is broken, and I'm working on the fix in #38. It is a massive refactoring of the plugin. I think will be better to wait for this PR. I'll try to finish it ASAP and you will be able to test the plugin locally.

[osipxd]

LGTM.
Thank you. I'll merge this PR after #38

[osipxd]

Thank you for your pull request. Plugin code base dramatically changed so I've implemented this feature myself