Consider Trivia Content before multiline members - fixes fsprojects#569

The pattern matching above uses nested `sepMember` function
to consider Trivia Content. The difference between those
pattern matching cases is that latter one matches on when
there are trailing non-multiline members.
There's some code duplication between those two now, which
I'm happy to refactor - feedback welcome.

src/Fantomas.Tests/ClassTests.fs

@@ -382,4 +382,19 @@ type Exception with
 
 type Exception with
     member inline __.FirstLine = __.Message.Split([| Environment.NewLine |], StringSplitOptions.RemoveEmptyEntries).[0]
-"""
+"""
+
+[<Test>]
+let ``No extra new lines between type members, 569``() =
+    let original = """type A() =
+
+    member this.MemberA =
+        if true then 0 else 1
+
+    member this.MemberB =
+        if true then 2 else 3
+
+    member this.MemberC = 0
+"""
+
+    formatSourceString false original config |> should equal original

src/Fantomas/CodePrinter.fs

@@ -1950,8 +1950,17 @@ and genMemberDefnList astContext node =
                 sepNlnConsideringTriviaContentBeforeWithAttributes xsh.Range attributes
             | _ -> sepNln
 
+        let sepMember (m:Composite<SynMemberDefn, SynBinding>) =
+            match m with
+            | Pair(x1,_) ->
+                let attributes = getRangesFromAttributesFromSynBinding x1
+                sepNln +> sepNlnConsideringTriviaContentBeforeWithAttributes x1.RangeOfBindingSansRhs attributes
+            | Single x ->
+                let attributes = getRangesFromAttributesFromSynMemberDefinition x
+                sepNln +> sepNlnConsideringTriviaContentBeforeWithAttributes x.Range attributes
+
         sepNln +> sepNlnFirstExpr 
-        +> col (rep 2 sepNln) xs (function
+        +> colEx sepMember xs (function
                 | Pair(x1, x2) -> genPropertyWithGetSet astContext (x1, x2)
                 | Single x -> genMemberDefn astContext x) 
         +> sepNln +> genMemberDefnList astContext ys