new connectivity spec

[askhamwhat]

this makes the change to the new connectivity specification and still allows for the old edge2verts format on construction.

New fields:

• edgesendverts = 2 x nedge array, edgesendverts(1,i) is starting vertex for edge and (2,j) is ending vertex.
• v2emat = sparse matrix, v2emat(i,j) is non-zero if edge i is connected to vertex j. it is 1 if edge i ends at vertex j, -1 if edge i starts at vertex j, and 2 if edge i starts and ends at vertex j. Note this is basically the same as edge2verts. This info is sometimes useful to have a fast method for finding info relevant to a specific vertex/set of vertices (see findregions/vertextract)