Implement tagWithName()

SwiftGit2/Repository.swift

@@ -283,6 +283,13 @@ final public class Repository {
 	}
 	
 	public func tagWithName(name: String) -> Result<TagReference> {
-		return failure()
+		return referenceWithName("refs/tags/" + name)
+			.flatMap {
+				if let tag = $0 as? TagReference {
+					return success(tag)
+				} else {
+					return failure()
+				}
+			}
 	}
 }

SwiftGit2Tests/RepositorySpec.swift

@@ -335,5 +335,17 @@ class RepositorySpec: QuickSpec {
 				expect(result.error()).notTo(beNil())
 			}
 		}
+		
+		describe("-tagWithName()") {
+			it("should return the tag if it exists") {
+				let result = Fixtures.simpleRepository.tagWithName("tag-2")
+				expect(result.value()?.longName).to(equal("refs/tags/tag-2"))
+			}
+			
+			it("should error if the branch doesn't exists") {
+				let result = Fixtures.simpleRepository.tagWithName("nonexistent")
+				expect(result.error()).notTo(beNil())
+			}
+		}
 	}
 }