File stale path references.

After rearranging the directory layout, some paths in documentation
needed updating.

Fix some typos too.

lib/cretonne/src/isa/riscv/settings.rs

@@ -3,8 +3,9 @@
 use settings::{self, detail, Builder};
 use std::fmt;
 
-// Include code generated by `meta/gen_settings.py`. This file contains a public `Flags` struct
-// with an impl for all of the settings defined in `meta/cretonne/settings.py`.
+// Include code generated by `lib/cretonne/meta/gen_settings.py`. This file contains a public
+// `Flags` struct with an impl for all of the settings defined in
+// `lib/cretonne/meta/cretonne/settings.py`.
 include!(concat!(env!("OUT_DIR"), "/settings-riscv.rs"));
 
 #[cfg(test)]