Update to Rust 2018 edition (#632)

* initial cargo fix run

* Upgrade cranelift-entity crate

* Upgrade bforest crate

* Upgrade the codegen crate

* Upgrade the faerie crate

* Upgrade the filetests crate

* Upgrade the codegen-meta crate

* Upgrade the frontend crate

* Upgrade the cranelift-module crate

* Upgrade the cranelift-native crate

* Upgrade the cranelift-preopt crate

* Upgrade the cranelift-reader crate

* Upgrade the cranelift-serde crate

* Upgrade the cranelift-simplejit crate

* Upgrade the cranelift or cranelift-umbrella crate

* Upgrade the cranelift-wasm crate

* Upgrade cranelift-tools crate

* Use new import style on remaining files

* run format-all.sh

* run test-all.sh, update Readme and travis ci configuration
fixed an AssertionError also

* Remove deprecated functions

lib/preopt/Cargo.toml

@@ -9,6 +9,7 @@ repository = "https://github.com/CraneStation/cranelift"
 categories = ["no-std"]
 readme = "README.md"
 keywords = ["optimize", "compile", "compiler", "jit"]
+edition = "2018"
 
 [dependencies]
 cranelift-codegen = { path = "../codegen", version = "0.26.0", default-features = false }

lib/preopt/src/lib.rs

@@ -27,9 +27,6 @@
 #[cfg(not(feature = "std"))]
 extern crate alloc;
 
-extern crate cranelift_codegen;
-// extern crate rustc_apfloat;
-
 mod constant_folding;
 
 use cranelift_codegen::{isa::TargetIsa, settings::FlagsOrIsa, CodegenResult, Context};