- construct from positions

- reset positions, minEdgeLen, find grid index

ENH: add accessor for obtaining the size of a single i-j-k dimension

- eg, obtain the 'i' dimension with any of these methods:

      ijkAddr.size(vector::X)
      ijkAddr.sizes().x()
      ijkAddr.sizes()[0]

- While a rectilinear mesh can be created with blockMesh, not every mesh
  created with blockMesh will satisfy the requirements for being a
  rectilinear mesh.

  This alternative to blockMesh uses a single block that is aligned
  with the xy-z directions and specifications of the control points,
  mesh divisions and expansion ratios. For example,

    x
    {
        points  ( -13.28 -0.10 6.0 19.19 );
        nCells  (  10  12 10 );
        ratios  ( 0.2   1  5 );
    }

    y { ... }
    z { ... }

  With only one block, the boundary patch definition is simple and the
  canonical face number is used directly. For example,

    inlet
    {
        type    patch;
        faces   ( 0 );
    }
    outlet
    {
        type    patch;
        faces   ( 1 );
    }

    sides
    {
        type    patch;
        faces   ( 2 3 );
    }

    ...

- After a mesh is defined, it is trivial to retrieve mesh-related
  information such as cell-volume, cell-centres for any i-j-k location
  without an actual polyMesh.

STYLE: remove -noFunctionObjects from blockMesh

- no time loop, so function objects cannot be triggered anyhow.