Refactor dem2pts

[ole]

To save space and to simplify the API refactor the two functions asc2dem and dem2pts as follows:

Rename dem2pts to netcdf_dem2pts and create new function something like

def dem2pts(filename, ....):

   basename, ext = os.path.splitext(filename)
   if ext == '':
      ext = 'asc' #Default

   if ext == 'asc':
      asc2dem(filename, ...)
      netcdf_dem2pts(filename, ...)
      os.remove(basename + '.dem'
   elif ext == 'dem':
      netcdf_dem2pts(filename, ...)