Release v3.1-RC2 (MobilityData#761)

* Add field city in station_information (MobilityData#704)

* Prepare to merge 'City in station_information' into master

* Future availability by vehicle (MobilityData#726)

* New vehicle_availability endpoint

* Update description to match id in vehicle_status

* Add pricing_plan_id and vehicle_equipment

* Make station_id conditionnally required

* Make station_id REQUIRED

* Add fare capping definition and example (MobilityData#745)

* Prepare v3.1-RC2 release

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Co-authored-by: Holger Bruch <[email protected]>

Update version numbers to v3.1-RC in the spec (MobilityData#639)

* Update version numbers to v3.1-RC in the spec
* Update 'added in v3.1-RC' for the new fields
* Add v3.1-RC to README

Update current version to v3.0 (MobilityData#625)

* Withdraw PR MobilityData#546 Floating Interval in price

* Withdraw PR MobilityData#457 Reservation Price

* Remove -RC and -RC2 from the spec

* Update current version number in spec

* Fix earlier version URLs

* Update current version in README to v3.0

* Set version history URL to Release Notes

Makes vehicle capacity at stations consistent between station_informa…

…tion and status (MobilityData#547)

* makes vehicle capacity at stations consistent

Modify examples to say v3.0-RC (MobilityData#502)

change examples from v3.0 -> v3.0-RC

* MobilityData#329 - Add vehicle drop off restrictions

* MobilityData#330 - Adding vehicle icons & brand information
* MobilityData#331 - Reserve time for vehicle types and pricing plans
* MobilityData#335 - Add pricing plans to vehicle types
* MobilityData#336 - Add fields for terms and privacy policy
* MobilityData#340 - Add field to designate stations that support vehicle charging
* MobilityData#349 - Add optional station_parking rule to geofencing_zones.json
* MobilityData#350 - Carsharing extension
* MobilityData#370 - ​​Extending vehicle_types.json
* MobilityData#386 - Versioning and Long Term Support
* MobilityData#400 - Changes to return_types field

* MobilityData#252 - Extend system_pricing_plans.json

* MobilityData#136 - Add vehicle type definitions

* MobilityData#219 - Add geofencing, virtual station, and dockless support
* MobilityData#261 - Aggregate available vehicle_types at a station

* MobilityData#25 - Add deep links for iOS, Android, and web apps

* MobilityData#181 - Add feed_contact_email field to system_information.json
* MobilityData#188 - GBFS documentation versioning and and feed conformance (adds gbfs_versions.json)

fixes to v2.3-RC2

makes default_pricing_plan_id optional to be non-breaking, corrects errors in code examples, labels new enums