Merge #207

207: Finish implementing char validation r=aochagavia a=aochagavia

The only thing missing right now are good integration tests (and maybe more descriptive error messages)

Co-authored-by: Adolfo Ochagavía <github@adolfo.ochagavia.xyz>

crates/ra_syntax/src/lib.rs

@@ -20,6 +20,7 @@
 #![allow(missing_docs)]
 //#![warn(unreachable_pub)] // rust-lang/rust#47816
 
+extern crate arrayvec;
 extern crate drop_bomb;
 extern crate itertools;
 extern crate parking_lot;