Add encoding size information to EncInfo.

Two new pieces of information are available for all encoding recipes:

- The size in bytes of an encoded instruction, and
- The range of a branch encoded with the recipe, if any.

In the meta language, EncRecipe takes two new constructor arguments. The
size is required for all encodings and branch_range is required for all
recipes used to encode branches.

lib/cretonne/src/isa/mod.rs

@@ -40,7 +40,7 @@
 //! The configured target ISA trait object is a `Box<TargetIsa>` which can be used for multiple
 //! concurrent function compilations.
 
-pub use isa::constraints::{RecipeConstraints, OperandConstraint, ConstraintKind};
+pub use isa::constraints::{RecipeConstraints, OperandConstraint, ConstraintKind, BranchRange};
 pub use isa::encoding::{Encoding, EncInfo};
 pub use isa::registers::{RegInfo, RegUnit, RegClass, RegClassIndex};