Add support for multiple hash types.

Add support for multiple hash types with negotiation of common hash types for comparison.

Manually rebased version of #277 (see discussion there)

hubic/hubic.go

@@ -207,6 +207,12 @@ func (f *Fs) UnWrap() fs.Fs {
 	return f.Fs
 }
 
+// Hashes returns the supported hash sets.
+// Inherited from swift
+func (f *Fs) Hashes() fs.HashSet {
+	return fs.HashSet(fs.HashMD5)
+}
+
 // Check the interfaces are satisfied
 var (
 	_ fs.Fs        = (*Fs)(nil)