Things to consider:
- BaseType[:] raises exception, we need BaseType.data

- Check GRADS plugin

Responses:
- netCDF
- Excel
- google spreadsheet api

WMS response:
- transparent gifs
- generate plots for inner variables of sequences, using color for value
- customize plots: line vs. points, animated vs. averages

2.3:
- simplify dap.dtypes and add client functionality (filters, proxies) to dap.proxy.BaseType, dap.plugins.sql.SequenceType, etc.
- rewrite parse_querystring and constrain (from dap.helper)
- rewrite all responses to dispatch based on ``isinstance``
- allow attributes to have a specific type (Float32, eg), when the plugin passes a ``numpy.array`` or ``array.array`` instead of a list.
- matlab plugin: use scipy.io.loadmat
