Sam/highlighted cfg paths

[slasser]

Add support for writing CFGs in which execution paths induced by a countermodel are highlighted.

[slasser]

Two things (at least) to discuss:

• Adding tests for get_taken_edges
• Whether Utils.print_diagnostics p.show overrides flags like --dump-cfgs when that condition is false

[slasser]

Update HTML documentation of --show=paths flag/argument:

https://github.com/draperlaboratory/cbat_tools/blob/master/docs/reference.html