cmd/doc: put blank lines around comment for types, etc.

Better layout.

Fixes #10859.

The issue suggests rearranging so the comment comes out
after the methods. I tried this and it looks good but it is less
useful, since the stuff you're probably looking for - the methods
- are scrolled away by the comment. The most important
information should be last because that leaves it on your
screen after the print if the output is long.

Change-Id: I560f992601ccbe2293c347fa1b1018a3f5346c82
Reviewed-on: https://go-review.googlesource.com/10160
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/doc/pkg.go

@@ -115,7 +115,7 @@ func (pkg *Package) emit(comment string, node ast.Node) {
 			log.Fatal(err)
 		}
 		if comment != "" {
-			pkg.newlines(1)
+			pkg.newlines(2) // Guarantee blank line before comment.
 			doc.ToText(&pkg.buf, comment, "    ", "\t", 80)
 		}
 		pkg.newlines(1)
@@ -352,6 +352,9 @@ func (pkg *Package) symbolDoc(symbol string) {
 		}
 		pkg.emit(typ.Doc, decl)
 		// Show associated methods, constants, etc.
+		if len(typ.Consts) > 0 || len(typ.Vars) > 0 || len(typ.Funcs) > 0 || len(typ.Methods) > 0 {
+			pkg.Printf("\n")
+		}
 		pkg.valueSummary(typ.Consts)
 		pkg.valueSummary(typ.Vars)
 		pkg.funcSummary(typ.Funcs)