New input decoders

[tspurway]

We have 2(ish) input decoders right now and only one is really solid (the json_decoder). Here's a good start:

• fixed_width (like csv, but with designated columns for each field)
• csv
• netCDF
• HDF5
• protocol buffer
• cap'n proto
• xml if there is still demand

Also, it would be nice to gather some good basic ETL preprocessors for various popular web and application servers, proxies, etc.

[oldmantaiter]

• NCSA common log format