Add code checking plugins

[ItsMajestiX]

It would be useful to check the code for bugs and poor coding practices before we put it on the robot. To accomplish this goal I have added four plugins to the build process of WPILib so that code must pass multiple analyses before the build succeeds.

• SpotBugs: Checks code for bugs and will fail build if it detects any. Provides an HTML report of what it finds.
• Error Prone: Similar to SpotBugs, checks code for bugs and will fail if it finds any. Does not have an HTML report, but gives suggestions in console.
• PMD: Checks code for poor coding practices and will fail if it finds any. Used by WPILib itself. Generates an HTML report.
• Checkstyle: We use the checkstyle extension for formatting (see Styleguide #5) so this plugin just makes sure those rules are followed. I have included Eric's checkstyle config so variables starting with m_ do not get flagged. Generates an HTML report.

[cpapplefamily]

Should your ReadMe overwrite all the sections or just be added to the list?

[ItsMajestiX]

It should not, so I just copied over the readme from main and added the section about error reports in that last commit.