Added support for partial active trail, handling terminal breadcrumb properly when menu active trail is set according to context (e.g., blog entries not attached by taxonomy). Some inline & online documentation cleanup.
NOTE: should do a full cache clear since 2 new services injected (router cache clear doesn't seem to be enough; new installations will work fine, as will reinstallations).
Code ported from MBAT sandbox; name changes only.
Fixed outstanding bugs (not recognising external links or home route).
Added Taxonomy Attachment feature, effectively extending active trail by taxonomy membership.
Allowed breadcrumb builder to fail over to others when it can't produce a breadcrumb.
Clarified online documentation in both settings and Help page.
Cleared up Drupal 7-isms in code and documentation.