Add data type hints to column and entry descriptions

[tahini]

Fixes #35

With this, it is expected that column and entry descriptions may contain an optional typing option, to explain what the data type is and, if available, what unit to use when formatting it.

This allow the server implementations to send raw data to the client, who would then have the option to format the data, but also the possibility to do some other actions, like sorting, or use the data for richer data interactions, as raw data may have a same meaning in different outputs, unlike pre-formatted data which may not allow such interaction.

Signed-off-by: Geneviève Bastien [email protected]