[feature request] Support rz/sz

[zxdong262]

Currently I use https://github.com/FGasper/zmodemjs, which have some issues when transfer big files, wondering if this project could provide support for rz/sz, so it can be used as a replacement to zmodemjs.

[lonnywong]

It shouldn't be difficult. But I'm busy working on trzsz right now.

If someone has time to work on it, please open a Pull Request.