Removing the exponentiation of ten improves the small case

Here are some average timings after this commit

Average initialization duration of Pi to 10 digits using std.BigInt = 878.02 ns
Average initialization duration of Pi to 10 digits using phi.Integer = 1394.12 ns
Average initialization duration of Pi to 50 digits using std.BigInt = 1177.84 ns
Average initialization duration of Pi to 50 digits using phi.Integer = 4473.6 ns
Average initialization duration of Pi to 100 digits using std.BigInt = 1644.74 ns
Average initialization duration of Pi to 100 digits using phi.Integer = 10299.5 ns
Average initialization duration of Pi to 1000 digits using std.BigInt = 24691.6 ns
Average initialization duration of Pi to 1000 digits using phi.Integer = 484568 ns

Here are the average timings from the previous run (see issue #37)

Average initialization duration of Pi to 10 digits using std.BigInt = 807.71 ns
Average initialization duration of Pi to 10 digits using phi.Integer = 1532.41 ns
Average initialization duration of Pi to 50 digits using std.BigInt = 1186.06 ns
Average initialization duration of Pi to 50 digits using phi.Integer = 4557.75 ns
Average initialization duration of Pi to 100 digits using std.BigInt = 1649.94 ns
Average initialization duration of Pi to 100 digits using phi.Integer = 10455.1 ns
Average initialization duration of Pi to 1000 digits using std.BigInt = 24782.2 ns
Average initialization duration of Pi to 1000 digits using phi.Integer = 487600 ns