Handle non-time-series data

[rileyhales]

make multiple classes?

• grids.Query.point, .multipoint, etc for queries which will produce a single value rather than a series
• other coordinate variables used instead of time?
• make a general Series class with an attribute indicating name of coordinate variable for the series?
• grids.TimeSeries returns grids.Series with the series coordinate variable attribute set to time (or the best guess for time)
• change the way the time steps are handled to be create the coordinate value index with one of the options being when the coordinate variable is time

[rileyhales]

This may require converting some of the query functions to static methods which get mixed-in to multiple other classes. Or make series the general class and TimeSeries and Query inherit from Series with specializations. Using classes is necessary to keep the code reasonably readable and maintainable rather than converting all of these to a series of functions.