adopt style guide for R code and examples

[jeremydouglass]

All R example code and documentation should largely conform to some consistent R code style guide -- ideally one that already exists, rather than the project developing its own.

Here is one example:

• Google's R Style Guide https://google.github.io/styleguide/Rguide.xml

Future documentation efforts would:

• choose an R style guide
• reference the chosen style guide in the wiki / documentation
• correct issues of style in example code to conform

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Example style consistency will be especially useful because some Processing.R users are more likely to be confused by readability issues, and may also be learning R syntax for the first time by way of Processing.

[jeremydouglass]

...it might also be worth reviewing all documentation and example R code for consistency using static analysis, e.g.:

• lintr: https://github.com/jimhester/lintr

[gaocegege]

I have imported coala which is a command line code linting tool. It will check the style of the code(both Java and R). Thanks to the awesome tool, the code has been prettified.

And I have added coala into ci. If there are some issues about code style in the code, the CI build will fail.

[jeremydouglass]

Great work!

[gaocegege]

😄 Thanks