Enable ‘hsndfile’ and add ‘hsndfile-vector’

New version of ‘c2hs’ is released where the bug that prevented
‘hsndfile’ from building is fixed according to maintainer of ‘c2hs’:

https://github.com/haskell/c2hs/issues/152#issuecomment-160433034

It also turns out that the package ‘hsndfile’ itself is of little use
without one ‘hsndfile-vector’ package.

This packages provides an instance of ‘Buffer’ type class using wrapper
around ‘Vector’ data type. Without the package it's not possible to
access individual audio samples.

build-constraints.yaml

@@ -1662,9 +1662,9 @@ packages:
     # "Andrew Lelechenko <andrew.lelechenko@gmail.com> @Bodigrim":
     #    - exp-pairs
 
-    # https://github.com/fpco/stackage/pull/980
-    # "Stefan Kersten <kaoskorobase@gmail.com> @kaoskorobase":
-    #     - hsndfile
+    "Stefan Kersten <kaoskorobase@gmail.com> @kaoskorobase":
+        - hsndfile
+        - hsndfile-vector
 
     "yihuang <yi.codeplayer@gmail.com> @yihuang":
         - tagstream-conduit
@@ -1682,7 +1682,7 @@ packages:
 
     "Henry J. Wylde <public@hjwylde.com> @hjwylde":
         - git-fmt
-    
+
     "Will Sewell <me@willsewell.com @willsewell_>":
         - benchpress