Xontrib-jump-to-dir

Refactoring. Replace partial to lambda.

* Added `jc ...` - jump to the directory where `*...*` command executed.
* Added `XONTRIB_JUMP_TO_DIR_WARNING` - show warnings from xontrib. Default `True`.

README improvements

Added `XONTRIB_JUMP_TO_DIR_SHORTCUT`.

Add __doc__

Publish package