Support for external data definition (e.g. CSV)

[zimmski]

It would be useful to add support for loading data from external sources e.g. a external CSV file could be loaded and be made available in the Tavor format. This could be done using a typed token:

$CSV CSV = file: path/to/file.csv

START = $CSV.Column("name")

Would print one entry of the column "name" from the given CSV file.

Additional type token arguments and token attributes could be added e.g. only load column x and y, only load row 1-10, define that the CSV has no header row.