Fix documentation of field add functions
Add field initialization
Add a string concatenation function

This is a utility function needed in writing vtk files.  Other
miscellaneous functions can be placed in bfam_util.{c,h} until
they find a better home.
Move vtk binary utility function to bfam_vtk.{c,h}

This move should allow multiple subdomain types to share this function.
Add vtk utility function for writing vector data
Add vtk utility function for writing scalar data
Add vtk output for point scalars and vectors