rename point<T>::value_type to coordinate_type

[jfirebaugh]

It would be useful if all geometry types had a member type identifying the T template parameter. point currently uses value_type for this, but that name is already taken for the types that inherit from vector such as line_string and multi_*. Let's use coordinate_type instead.

[jfirebaugh]

cc @artemp @springmeyer

[artemp]

@jfirebaugh - Yes, good call and I already had to do it in https://github.com/mapnik/mapnik/blob/geometry-refactor/include/mapnik/geometry/point.hpp#L31.

I'd like to keep future developer happy - why don't we shorten name to be coord_type to avoid extra typing ?

[jfirebaugh]

Since it's something that you're likely reading much more often then typing, I think it's better to use the full word here. It's only one more character than container_type which we're not abbreviating.

[springmeyer]

👍