The coordinate system was unable to support types that prohibited
redim or retype operations. Additionally, the `tags' type used for
providing named data parameters was unwiedly.
We remove much of the dependance on template template parameters in the
defined operations and instead define these in terms of a template
specialisation of is_coord.
The tag types were replaced with direct specialisation of the `store'
struct by the primary type, and passing this type through use of the
CRTP.
