Rename CONTRIBUTORS to MAINTAINERS and update list to current state (#435)

We'd like a way for people to know who they can ping for help on PRs and
issues, but we want to avoid being automatically assigned to PRs via
something like CODEOWNERS. Instead, we've opted to list the maintainers
of the project in a new MAINTAINERS file.

We opted to change from CONTRIBUTORS to MAINTAINERS since we believe
that contributors are already acknowledged via the `Contributors` tab on
GitHub and in the release notes we make for each new release.

In the future, the MAINTAINERS file can be extended to include
additional maintainers and past maintainers can continue to be
recognized for their work.

MAINTAINERS.txt

@@ -1,23 +1,26 @@
-This file contains a list of contributors who have made meaningful changes to this repository.
-Please add your name and GitHub handle to this file as an optional step in the contribution process for attribution.
-Email is not required.
+This file contains a list of maintainers and past maintainers who have made meaningful changes to this repository.
 
-### Contributors
+### Maintainers
 
 Aditya Ramani (adityaramani)
-Agam Dua (agamdua)
+AJ Emory (ajemory)
 Danny Canter (dcantah)
 Dmitry Kovba (dkovba)
 Eric Ernst (egernst)
-Evan Hazlett (ehazlett)
-Gilbert Song (gilbert88)
-Hugh Bussell (hughbussell)
 John Logan (jglogan)
 Kathryn Baldauf (katiewasnothere)
 Madhu Venugopal (mavenugo)
 Michael Crosby (crosbymichael)
-Nandha Reddy (nandsha)
+Raj Aryan Singh (realrajaryan)
 Sidhartha Mani (wlan0)
+Yibo Zhuang (yibozhuang)
+
+
+### Emeritus maintainers
+
+Agam Dua (agamdua)
+Evan Hazlett (ehazlett)
+Gilbert Song (gilbert88)
+Hugh Bussell (hughbussell)
 Tanweer Noor (tanweernoor)
 Ximena Perez Diaz (ximenanperez)
-Yibo Zhuang (yibozhuang)