* [enhancement] Thanks to [@HofiOne](https://github.com/HofiOne), `ttab` now supports new macOS-focused options, `-h`, `-v`, `-c`, and `-i`,
    which notably includes support for splitting the current tab horizontally (`-h`) or vertically (`-v`) in iTerm2.
  * [fix] Attempts to use options that are not supported in the target terminal now consistently result in errors.
  * [breaking change] Since `-h` now requests horizontal splitting, it can no longer be used to invoke help; use `--help` instead.