Support syntax highlighting implementations based on whether they pass all test cases for given keywords

This is low priority / longer term, especially given it likely depends on #27 and maybe #24 as well as some general library for semantically understanding schemas -- but nonetheless, for that day in the future:

When running `bowtie validate` (or any other ad hoc validation) and comparing implementation results, it would be helpful to see whether an implementation is known to be "fully compliant for the given schema" or not -- in other words, given a schema `S`, if the implementation passes the test suite for all keywords contained (recursively) in S, call it "compliant" and highlight it differently in the terminal (and possibly UI). This makes it easier to see when implementations differ on results even though they pass the suite.

#23 is likely also relevant in that maybe it can make use of this information as *input*.

Start at the `bowtie validate` implementation-comparison flow and review issues #27, #24, and #23 for dependencies and expected inputs. Determine how keyword coverage for a schema could be assessed across test results; done means implementations can be identified as compliant for all recursively contained keywords and highlighted differently in terminal output, with any UI implications understood.

Written by the indexing model from the issue text.