Added table gtfs_headway and began work calculating 8 types of headway (for each day of the week = 56 values); variant 4a is underway.
Added function to calculate transit vehicle headways from an array of vehicle arrivals at stop. This can be used for all 8 headway definitions.
Headway variant 4a commits correctly to database.
Calendar dates, mode and route restrictions are now considered for gtfs_headway, 4a variant.
Headway variation 3a complete
Fixed errors in database writing for variant 3a. Output verified as correct and distinct from 4a.
Update README.md
Added support for headway definition 2a
Added documentation for headway definition 2a
Added support and documentation for headway definition 1a; equivalent vehicles are defined as being of the same route and route variant.
Headway variants 1b, 2b, 3b, and 4b are now all supported and documented.
Merge pull request #6 from alpha-beta-soup/gtfs-headway-rec

Gtfs headway rec