Add a rough sketch of References and Branches

SwiftGit2/References.swift

@@ -6,4 +6,56 @@
 //  Copyright (c) 2015 GitHub, Inc. All rights reserved.
 //
 
+/// A reference to a git object.
+public protocol ReferenceType {
+	/// The full name of the reference (e.g., `refs/heads/master`).
+	var longName: String { get }
+	
+	/// The short human-readable name of the reference if one exists (e.g., `master`).
+	var shortName: String? { get }
+	
+	/// The OID of the referenced object.
+	var oid: OID { get }
+}
+
+/// A generic reference to a git object.
+public struct Reference: ReferenceType {
+	/// The full name of the reference (e.g., `refs/heads/master`).
+	public let longName: String
+	
+	/// The short human-readable name of the reference if one exists (e.g., `master`).
+	public let shortName: String?
+	
+	/// The OID of the referenced object.
+	public let oid: OID
+}
+
+/// A git branch.
+public struct Branch: ReferenceType {
+	/// The full name of the reference (e.g., `refs/heads/master`).
+	public let longName: String
+	
+	/// The name of the remote this branch belongs to, or nil if it's a local branch.
+	public let remoteName: String?
+	
+	/// The short human-readable name of the branch (e.g., `master`).
+	public let name: String
+	
+	/// A pointer to the referenced commit.
+	public let commit: PointerTo<Commit>
+	
+	// MARK: Derived Properties
+	
+	/// The short human-readable name of the branch (e.g., `master`).
+	///
+	/// This is the same as `name`, but is declared with an Optional type to adhere to
+	/// `ReferenceType`.
+	public var shortName: String? { return name }
+	
+	/// The OID of the referenced object.
+	///
+	/// This is the same as `commit.oid`, but is declared here to adhere to `ReferenceType`.
+	public var oid: OID { return commit.oid }
+}
+