Remove the Foo/flatFoo abstraction in the types package.

Fixes #24.

types/string.go

@@ -1,14 +1,34 @@
 package types
 
-type String interface {
-	Value
+import (
+	"github.com/attic-labs/noms/ref"
+)
 
-	Blob() Blob
-
-	// Slurps the entire string into memory. You obviously don't want to do this if the string might be large.
-	String() string
+type String struct {
+	s  string
+	cr *cachedRef
 }
 
 func NewString(s string) String {
-	return flatString{s, &cachedRef{}}
+	return String{s, &cachedRef{}}
+}
+
+func (fs String) Blob() Blob {
+	return NewBlob([]byte(fs.s))
+}
+
+func (fs String) String() string {
+	return fs.s
+}
+
+func (fs String) Ref() ref.Ref {
+	return fs.cr.Ref(fs)
+}
+
+func (fs String) Equals(other Value) bool {
+	if other == nil {
+		return false
+	} else {
+		return fs.Ref() == other.Ref()
+	}
 }