Migrate and update XSLTs for publishing

[wendellpiez]

There is OSCAL WIP here, on publishing XSLTs: https://github.com/wendellpiez/OSCAL/tree/publishing-v0dot1

Additionally, there are (at least) two Issues in the OSCAL repo tracking this work: usnistgov/oscal#574 and usnistgov/OSCAL#630.

This work needs to be completed (to a stable point) and documented.

Acceptance Criteria

• XSLTs for catalogs and resolved profiles work effectively on SP800-53 examples, both rev 4 and rev 5, producing HTML and PDF, in freely distributable tools (SaxonHE and FOP)
• XSLTs for other document types (e.g., SSP) reflect best-reasonable efforts given available samples or demo docs
• User docs explain how to use the XSLTs, for example using Saxon from a command line
• A PR into this repo includes this work

NB: to produce PDFs, Saxon alone is not enough: users also need Apache FOP or another XSL-FO formatting engine. While we may not wish to distribute these packages, we may wish to provide some level of support, for example via maven.

[wendellpiez]

@david-waltermire-nist this Issue in the oscal-tools repo, should we close it?

Same work item as usnistgov/OSCAL#630

[david-waltermire]

We can close this when usnistgov/oscal-xslt#9 is done.

[wendellpiez]

See also work being done in the FedRAMP automation repository on SSP rendering: https://github.com/GSA/fedramp-automation

[wendellpiez]

Suggest we spin off a new Issue for SSP preview mentioned here, and close this Issue.

[wendellpiez]

An SSP Preview XSLT is now described on usnistgov/OSCAL#43.