1. Adds the `--log-level LOG_LEVEL` flag to the CLI. This flag can be
given `error`, `warn`, `info`, `progress`, `debug` as argument to filter
the logged messages.
2. Removes the `--only-errors` flag.
3. Adds the `--ide-end-error-char CHAR`, which receives a character as
an argument, which is appended to the end of error messages. This is
handy to facilitate parsing of errors messages from the ide. This
functionality was previously embeded in the old `--only-errors` flag.
