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/codegen/meta-python/cdsl/xform.py

@@ -394,7 +394,7 @@ class XFormGroup(object):
             # table referring to it.
             return self.name
         else:
-            return '::legalizer::{}'.format(self.name)
+            return 'crate::legalizer::{}'.format(self.name)
 
     def legalize(self, src, dst):
         # type: (Union[Def, Apply], Rtl) -> None