[Open-scap] Increase depth of table of contents?

[Shawn Wells]

'xccdf generate guide' currently creates HTML with a table of contents 
depth of two. Could we either:

a) Increase the default table of contents depth? For SSG, a depth of 3 
or 4 seems good. Ref code:
https://github.com/OpenSCAP/openscap/blob/maint-1.2/xsl/xccdf-guide-impl.xsl#L468

b) Create CLI argument for user-defined table of contents depth?

For the SSG content, generally XCCDF rules are nested 3 groupings down 
and are not displayed in the default Table of Contents setting.