Add support for multiple prime meridians > multiple lat/longs

[kintopp]

Several different prime meridians were in active use in the period most relevant to EM Places (1500-1800). Of these, cartographically, the (arguably) most important ran through the Canaries, the Cape Verde, and the Azores islands. For example, location references in Diderot's Encyclopedie assume the meridian runs through the Ferro Islands in the West Canaries.

For details, see: Jonkers, A.R.T., 2005. "Parallel meridians: Diffusion and change in early-modern oceanic reckoning," in: Noord-Zuid in Oostindisch perspectief, ed. J. Parmentier. The
Hague: Walburg, pp.17-42