feat: sql handlers for custom media types

* test text/html and drop HtmlRawOutputSpec.hs
* all tests passing, removed all pendingWith
* make functions compatible with pg <= 12
* move custom media types tests to own spec
* anyelement aggregate
* apply aggregates without a final function
* overriding works
* overriding anyelement with particular agg
* cannot override vendored media types
* plan spec works with custom aggregate
* renamed media types to make clear which ones are overridable
* correct content negotiation with same weight
* text/tab-separated-values media type
* text/csv with BOM plus content-disposition header

test/spec/Feature/OpenApi/RootSpec.hs

@@ -13,7 +13,6 @@ spec :: SpecWith ((), Application)
 spec =
   describe "root spec function" $ do
     it "accepts application/openapi+json" $ do
-      pendingWith "TBD"
       request methodGet "/"
         [("Accept","application/openapi+json")] "" `shouldRespondWith`
         [json|{
@@ -21,3 +20,12 @@ spec =
            "info": {"title": "PostgREST API", "description": "This is a dynamic API generated by PostgREST"}
           }|]
         { matchHeaders = ["Content-Type" <:> "application/openapi+json; charset=utf-8"] }
+
+    it "accepts application/json" $ do
+      request methodGet "/"
+        [("Accept","application/json")] "" `shouldRespondWith`
+        [json|{
+           "swagger": "2.0",
+           "info": {"title": "PostgREST API", "description": "This is a dynamic API generated by PostgREST"}
+          }|]
+        { matchHeaders = ["Content-Type" <:> "application/json; charset=utf-8"] }