Rename: primitives/sr-std -> primitives/sp-std (#4327)

* primitives/sr-std -> primitives/std

* fix

* fix conflict

* rstd -> sp-std

* git mv

* fix review

* fix merge

substrate/primitives/std/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "sp-std"
+version = "2.0.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[features]
+default = ["std"]
+std = []