Pipeline Step Documentation Generator improvements

The Jenkins Pipeline Step reference is difficult to read, even to the initiated, mostly due to its format. This project aims to improve the way the documentation is formatted.

For example, when you read the readFile step documentation, the documentation format makes it difficult to see that the obvious usage is : readFile(String file, String encoding). When you read the checkout documentation, you are shown a single web page that when printed would be 62 pages long. That is too large a page for usable navigation. We should consider logical partitions of that page, possibly with a single page per SCM provider (like checkout-git, checkout-p4, checkout-svn, checkout-cvs).

For this project, the student is expected to study the documentation generator code base, the documentation feedback from readers, and to propose enhancements to the documentation generator code to improve the format, layout, and readability of the documentation published on-line. The student is not expected to contribute to the content of the documentation, however, technical additions that enhance the discoverability of the documentation via annotations or other special markup is considered valid for a coding project.

The student is also expected to study Stapler and Jelly, as these technologies are used to capture documentation as well. Documentation can be extracted from Stapler and Jelly.

A potential stretch goal could be something like an embedded pipeline steps generator, though that might be outside the scope of the website

Examples of remote documentation: * Pipeline: AWS steps adds documentation to the README * JIRA Pipeline steps keeps their documentation in their repo, and displays it as a weblink.