Bump mobsql dep: fix for custom GTFS feeds 'active' status
Bump mobsql dep to v0.9.0
Add databaseq example to CLI userguide; minor various other doc fixups
Fix stops CLI subcommand; nil filtering was broken as not behavior of loader
Add support for filtering nils in dbquery.LoadStopWalks
Fix query for stop walks extraction limiting based on dist_km filter
Link to diagrams from godoc
Add routing dataflow pattern diagram
Rework & fill out most of the remaning godoc
Fix doc SVG diagrams rendering
Add overal system diagram to doc