Improve the flexibility of providing input coordinates to DataSet object

[ljlamarche]

Currently, all spatial coordinates input into the DataSet class must have the same shape. Some users may prefer to provide arrays for latitude and longitude coordinates but a single value for altitude (this is more intuitive for many optical datasets that assume a particular emission altitude, for instance). Alternatively, radar data will sometimes have an elevation and azimuth angle for a set number of beams, but then an array of ranges that need to be applied to all the beams equally.

Will have to be careful to implement these kinds of features in a reasonable way so that they are helpful for users who often make these kinds of assumptions, but do not limit the flexibility and intuitive use of procedures for other users.