only unsafe versions of some functions in docs

[visr]

There is a nice docstring for unsafe_gdalwarp here: https://github.com/yeesian/ArchGDAL.jl/blob/0c57b987082aec3dbe2999ec5e5a729e0ebdc3fc/src/utilities.jl#L46-L58. It is in the documentation here: https://yeesian.com/ArchGDAL.jl/dev/reference/#ArchGDAL.unsafe_gdalwarp

This code wraps a list of unsafe functions in a finalizer, to make them safe, so gdalwarp is defined here: https://github.com/yeesian/ArchGDAL.jl/blob/0c57b987082aec3dbe2999ec5e5a729e0ebdc3fc/src/context.jl#L192-L222

gdalwarp is probably the version most people should use. Right now it has no docstring however. We should find a way to give them docstrings as well, and perhaps even leave out the docstrings of the unsafe versions in the docs. Right now users using the docs will only find unsafe_gdalwarp, and don't know that gdalwarp also exists.