Mosquitto mqtt rust bindings

Hi All,

I've been reading rust for about 4 months but this is the first time that I'm writing something serious and looking forward to maintain it. I wanted a stable mqtt client library for one of my projects. There are some native rust libraries available but none of them seems to be maintained. So I've decided to write rust wrapers for mosquitto mqtt C library which is available almost every where including router distributions like openwrt. Can someone please review this code and let me know if this can be improved?

PS: Is this the correct place to ask for code reviews?