[Feature] Allow using nvtop as a library for other apps

[pktiuk]

I think this app does a great job as a tool for monitoring GPU usage for different vendors.
But a CLI app is not always something people need.

I think, that with minor modifications this repository could be also used for building just a C (or C++) library libnvtop, which could be used by other developers to create other apps allowing monitoring GPUs.
It could be used as a base for plugin for existing system monitors, and standalone GUI monitors, it could be used for monitoring servers used for machine learning with cockpit addon, or with Performance Co-Pilot, etc.

Example with grafana-pcp: