Improve / write docs

[jdroenner]

The state of the documentation in this crate is not as it should be. This is a task is also ideal for new contributors. Most of the time the docs of the wrapped gdal-sys method will be enough to derive a methods doc.

[metasim]

@jdroenner By this:

Most of the time the docs of the wrapped gdal-sys method will be enough to derive a methods doc.

are you suggesting (as a contribution) the gdal doxygen docs be copied over into the rust code?

[metasim]

I just rebuilt the documentation with bindgen version 0.59.2, and it seems a lot more documentation is getting injected than what's in docs.rs:

[lnicola]

I remember a bindgen "feature" causing comments to be included or not in the generated bindings based on the location of the GDAL headers.