cadfa4152b
Colored exception output is now disabled by default and configurable through `hy.errors._hy_colored_errors` and the environment variable `HY_COLORED_ERRORS`. Likewise, Hy model/AST color printing is now configurable and disabled by default. The corresponding variables are `hy.models._hy_colored_ast_objects` and `HY_COLORED_AST_OBJECTS`. Closes hylang/hy#1429, closes hylang/hy#1510.