Alternate Input Sources instead of CSV

[jrawbits]

Add a mapping option that will seek a .csv input file (from 'Inp' specification) in some other location.

Easy on the surface: just say where to look and using what input driver format.

Rather than working at the file level, we might consider making the InputPath entries more expansive - the directory amounts to a "connection" in which to seek the "table". So InputPath would become a list instead of a vector and we'd need a functional interface (usable perhaps with lapply) to extract tables. That could be backward compatible just by looking at is.character(InputPath) - if it's a list, then each element specifies a driver, a connection string, and a function for converting the requested table name to some tabular object within the connection. Could perhaps submerge that into an API, so the list contains an R "object" with callable functions to open the connection and retrieve the table. Then use ViEIO to furnish those objects (prefabricated for common data sources).