Rename 'cton_*' library names to match the 'cretonne_*' crate names.

This renames `cton_frontend` to `cretonne_frontend` and so on.

This fixes the first part of #287.

lib/wasm/src/code_translator.rs

@@ -26,7 +26,7 @@ use cretonne::ir::condcodes::{FloatCC, IntCC};
 use cretonne::ir::types::*;
 use cretonne::ir::{self, InstBuilder, JumpTableData, MemFlags};
 use cretonne::packed_option::ReservedValue;
-use cton_frontend::{FunctionBuilder, Variable};
+use cretonne_frontend::{FunctionBuilder, Variable};
 use environ::{FuncEnvironment, GlobalValue};
 use state::{ControlStackFrame, TranslationState};
 use std::collections::{hash_map, HashMap};