Update copyright notices

[wwahammy]

I realized that we didn't update the copyright notices in LICENSE.txt. As the MIT license requires us to keep previous copyright notices, I've kept Authy's and I've made the following additions:

• Midwest Access Coalition since the copyright of @camckin10 and I are assigned under contract to them. (And likely @BintLopez's is too)
• jayywolff since we often use his repo as reference
• A general line to cover the copyright of other contributors to the project.

I also removed the specific copyright line from the README since it just references the LICENSE.txt and it seems redundant.

NOTE: I purposely don't add a copyright year to the lines we can control. I've always been advised that the year is unnecessary. Someone has to keep it up to date and it doesn't add anything, the key is knowing who is licensing the work.

[BintLopez]

🦑