Proposed updated CODEOWNERS to allow better review notifications

Based on current pull request feedback and maintenance trends I'm suggesting
these rules to get the right people on the reviews by default.

Closes delta-io#1553

.github/CODEOWNERS

@@ -1,4 +1,6 @@
-* @houqp @xianwill @wjones127 @fvaleye @roeap @rtyler @mosyp
+rust/ @wjones127 @roeap @rtyler
 proofs/ @houqp
-python/ @wjones127 @fvaleye @rtyler @roeap @houqp
+python/ @wjones127 @fvaleye @roeap
 tlaplus/ @houqp
+.github/ @wjones127 @rtyler
+docs/ @MrPowers