Usable as a library?

[StyXman]

I would like to use this code as a Python module to enable MBTiles writing to a tool I use to render tilesets. The problem is that some parts of the module (all inside the mbutil directory) is assuming it's only part of the mb-util script. For instance:

https://github.com/mapbox/mbutil/blob/master/mbutil/util.py#L41

This should be handled in the util's code. Probably others are to follow.

On the other hand, there are no functions to be able to read/write individual tiles, which could be refactored from the current code.

I plan to start a PR soon, but I would like to hear your opinions on this.

[tmcw]

Happy to accept a PR implementing a change that would make this usable as a library!

[tmcw]

Closing; happy to accept a PR.