Updated revision history for CHANGES.md

[sccmcca]

Updated GTFS revision history for transit/gtfs/CHANGES.md as of May 28, 2020. The revision history was last updated January 2019, with some historical entries missing.

If you have feedback or if I missed anything major, please let me know.

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[barbeau]

concision -> conciseness

[barbeau]

This file has historically been used only for static GTFS revision history.

However, unless I'm missing something, it looks like the Google website that has the GTFS-RT revision history:
https://developers.google.com/transit/gtfs-realtime/guides/revision-history

...never made it into the GitHub repo. There is an equivalent CHANGES.md for GTFS-RT:
https://github.com/google/transit/blob/master/gtfs-realtime/CHANGES.md

...but it's missing the revision history.

So we need to decide if we keep all GTFS and GTFS-RT revisions in the same document, or if we split them across two files.

In any case, the Google website revision history should be migrated into this GitHub repo somewhere.

[sccmcca]

Good catch. I meant to include only the updated revision history for static GTFS only.

I noticed as well that there was no GTFS-RT revision history at https://github.com/google/transit/blob/master/gtfs-realtime/CHANGES.md

I would be for adding it there.

[drewda]

@scmcca thanks for helping with this housekeeping

@barbeau I for one think that it would be most useful to track static and RT changes in separate places (still important to have both)

related #215

[sccmcca]

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