init covariance and glasso

- 'glasso' is method to estimate sparse covariance/precision matrices from
  sample data. I am not the author of 'glasso', but in agreement with the author
  I add this package. The author may take ownership at a later time.
  See https://github.com/kaizhang/glasso/issues/1.

- 'covariance' provides shrinkage based estimators for the same problem and also
   a wrapper around 'glasso'.

This solves issue https://github.com/commercialhaskell/stackage/issues/6196.

I also sorted the packages I maintain.

build-constraints.yaml

@@ -4556,18 +4556,20 @@ packages:
         - cabal-appimage
 
     "Dominik Schrempf <dominik.schrempf@gmail.com> @dschrempf":
-        - pava
+        - circular
-        - elynx-nexus
+        - covariance
+        - dirichlet
+        - elynx
         - elynx-markov
+        - elynx-nexus
         - elynx-seq
         - elynx-tools
         - elynx-tree
+        - glasso
+        - mcmc
+        - pava
         - slynx
         - tlynx
-        - elynx
-        - mcmc
-        - dirichlet
-        - circular
 
     "Eric Rochester <erochest@gmail.com> @erochest":
         - text-regex-replace
@@ -6719,9 +6721,6 @@ packages:
       # https://github.com/commercialhaskell/stackage/issues/6195
       - miso < 1.8
 
-      # https://github.com/commercialhaskell/stackage/issues/6196
-      - mcmc < 0.6.1
-
 # end of packages
 
 # Package flags are applied to individual packages, and override the values of