API for creating a cloud file by uploading it

[pjbull]

We have download_to to make it easy to copy a file from the cloud to the local filesystem. We don't have an equivalent upload or upload_from or copy_from (naming is hard) method to easily create a cloud file from a local one.

E.g

# path that does not exist yet
p = CloudPath("az://container/dir/new_file.txt")

#  copies "my_local_text_file.txt" to the path specified by p
p.upload("my_local_text_file.txt")

[jayqi]

I like upload_from. It has symmetry with download_to. We also want to distinguish uploading a local file vs. copying from another cloud path (#108).