Fix folder names in primitives (#4358)

* sr-arithmetic -> arithmetic

* sr-sandbox -> sandbox

* primitives/sr-staking-primitives -> primitives/staking

* primitives/sr-version -> primitives/version

* primitives/block-builder/runtime-api -> primitives/block-builder

substrate/primitives/arithmetic/src/lib.rs

@@ -0,0 +1,44 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Minimal fixed point arithmetic primitives and types for runtime.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+/// Copied from `sp-runtime` and documented there.
+#[cfg(test)]
+macro_rules! assert_eq_error_rate {
+	($x:expr, $y:expr, $error:expr $(,)?) => {
+		assert!(
+			($x) >= (($y) - ($error)) && ($x) <= (($y) + ($error)),
+			"{:?} != {:?} (with error rate {:?})",
+			$x,
+			$y,
+			$error,
+		);
+	};
+}
+
+pub mod biguint;
+pub mod helpers_128bit;
+pub mod traits;
+mod per_things;
+mod fixed64;
+mod rational128;
+
+pub use fixed64::Fixed64;
+pub use per_things::{Percent, Permill, Perbill, Perquintill};
+pub use rational128::Rational128;