Enable the stencil for framebuffers + 50 lines of nightmares

[Frosty-J]

This pull request changes up toTextureRegion() a bit.

• Enables the stencil buffer on the framebuffer to improve rendering.
• Negative-size TVGs now behave correctly.
• Negative- and zero-size TVGs no longer cause it to crash. I forgot this part. Will fix in another PR.
• Handling of float to int conversion for framebuffer size has been improved.
• Added a supersampling overload to work around FrameBuffer's lack of antialiasing support (it's infinitely faster than tvg-render but subject to texture size limits).
• Removed the clear() because new framebuffers are always empty (in my experience) and clearing them takes time.
• Made some subjective changes that you should just revert without discussion if you disagree with.

Known issues:

• viewport.update() ignores the width and height passed into it. This has nothing to do with me removing viewport.apply() - it doesn't work with that either.
• When supersampling pirate.tvg, his face is smoothened out nicely but the edges of his face are jaggy. Putting him on a solid background fixes this. Something is wrong with alpha. I've tried layering a semi-transparent rectangle down and that has the correct alpha, so I really don't know what is going on.

I'm unsure what the state is in tests because Assertions.assertTrue(lock.await(5, TimeUnit.SECONDS)); and its friends fail. Hopefully all is well. It's not identical to my test code due to a difference in Java versions and I didn't figure out how to do an mvn install on this library's source code.

This pull request is feature creep, considering it was only supposed to be a single-line change. You may just want to copy the line I came here for, with its original name of buffer, into the repository for now, since it's the important fix.

https://github.com/lyze237/gdx-TinyVG/blob/7db63a4998af58c785c9653965dd3d934e830d62/src/main/java/dev/lyze/gdxtinyvg/TinyVGIO.java#L28

[lyze237]

You should be able to run gradlew publishToMavenLocal to install it to .m2 locally.

[lyze237]

Thanks for the pull request though, I've run through all test and it looks like all is good. Soo lgtm. :)