Compiler and command-line error messages now reflect their Python counterparts.
E.g. where Python emits a `SyntaxError`, so does Hy; same for `TypeError`s.
Multiple tests have been added that check the format and type of raised
exceptions over varying command-line invocations (e.g. interactive and not).
A new exception type for `require` errors was added so that they can be treated
like normal run-time errors and not compiler errors.
The Hy REPL has been further refactored to better match the class-structured
API. Now, different error types are handled separately and leverage more base
class-provided functionality.
Closeshylang/hy#1486.