Parse binary headers with file paths (#55)

Some patches may include one or more file paths as part of the binary
header when there is no binary data. Git accounts for this by only
checking the prefix and suffix of the line, but I missed that logic when
implementing this originally.

gitdiff/binary_test.go

@@ -25,6 +25,16 @@ func TestParseBinaryMarker(t *testing.T) {
 			IsBinary: true,
 			HasData:  false,
 		},
+		"binaryFileNoPatchPaths": {
+			Input:    "Binary files a/foo.bin and b/foo.bin differ\n",
+			IsBinary: true,
+			HasData:  false,
+		},
+		"fileNoPatch": {
+			Input:    "Files differ\n",
+			IsBinary: true,
+			HasData:  false,
+		},
 		"textFile": {
 			Input:    "@@ -10,14 +22,31 @@\n",
 			IsBinary: false,