Expose functions to get GPS latitude, longitude and altitude separately

[jonas-hagen]

Suggestion: A possible (partial?) solution to #42.

The gexiv2 functions to access GPS latitude, longitude and altitude are exposed. The already present function get_gps_info() returns None if the altitude is not set. These newly exposed functions allow access to latitude and longitude in this (quite common) case.

[felixc]

Hey!

Thanks for the PR — I especially appreciate that you added example code for it :)

Like I mentioned in #42, I'm not sure I'm understanding the root cause correctly, so let's discuss there before merging this — but it certainly looks good to me and I'm in favour of landing it.

Could you please also add yourself to the CONTRIBUTORS.md file?

[jonas-hagen]

Thanks for your comments! I will then update the PR.

[felixc]

Thanks for presenting the two options. I've gone with the other alternative (though with a variant implementation), so I think we can close this now. #69 landed instead. Please comment on #42 if you think we should reconsider this approach instead!