Upload arguments

[perrygeo]

For compatibility with mapbox-upload, the current upload CLI arguments follow suit. However, we might want to consider tweaking the design a bit

1. mapbox upload DESTINATION-tileset and SOURCE-file - the current ordering is opposite what one would expect from unix tools like cp which generally follow the cmd source destination pattern. Switch 'em?
2. we should consider making --name default to the basename of the file rather than None. This avoids having a bunch of "Untitled" tilesets in studio should you forget to supply the optional name.
3. we should also consider making the username in the tileset id optional. We can infer the username from the access token and prepend it if there is no username supplied. This would help to write more reusable bash scripts intended to be run with different accounts.

Should we implement these changes? If so, do they belong here or could some be baked into SDK behavior?

[perrygeo]

fixed with #68