Create Macro for Implementing SlotRange (#2788)

* Macro for generating `SlotRange`

* remove test code

* refactor slots into crate

* add no_std flag

* finish macro

* make compile

* fix copyright date

* don't assume lease periods per slot

* Update runtime/common/Cargo.toml

* Apply suggestions from code review

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* fixes

* Update lib.rs

* tests

* Move consts into struct

* docs

* fix compile

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update Cargo.lock

* Update runtime/common/src/slot_range.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* fixes

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

polkadot/runtime/common/slot_range_helper/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "slot-range-helper"
+version = "0.8.30"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+paste = "1.0"
+parity-scale-codec = { version = "2.0.0", default-features = false, features = ["derive"] }
+sp-std = { package = "sp-std", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"sp-std/std",
+	"parity-scale-codec/std",
+	"sp-runtime/std",
+]