Add processing 3.5.3 new methods

[berinhard]

Fixes #336

This PR add the new methods added by Processing 3.5.3 and also enable the use of push and pop as context managers.

I struggled with the build process, but I wasn't successful. I'm always running into this error:

BUILD FAILED
/home/bernardo/workspace/processing.py/build.xml:216: The following error occurred while executing this line:
/home/bernardo/workspace/processing/build/build.xml:57: Unsupported Java version: 10.0.2. To build, make sure that Java 8 (aka Java 1.8) is installed.

Even though I have Java 8 installed and my JAVA_HOME env var set to use my Java 8 installation. I'm not that familiar with Java and a lot of posts I read on Stackoverflow suggests me to use an IDE to build instead of the command line.

[jdf]

Could you add a test that exercise push() and pop()? I don't even know what they do. :)

[jdf]

I'm guessing there's a java 10 in your $PATH.

[berinhard]

@jdf PR updated =]

I added new tests for the circle method and also for the push/pop as well. They're passing for me as you can see in this print:

I also have a question. Should I also add those new methods to the keywords.txt file?

[jdf]

Nice work; thank you.

[jdf]

Oops; missed your question. Yes, it would be great to have new keyword lighlighting too.