Simple model of itsdb tables and rows

[goodmami]

ItsdbProfile.read_table() should perhaps return a basic ItsdbTable instance, which might just be a wrapper around a list. Similarly, it could be a list of ItsdbRows, which wraps another list (not a dict). Then functions like select() could be on these classes.

One benefit, besides a more friendly API, is that joined tables can be more manageable, with names, easier column selection, etc.

[goodmami]

I think there was a reason I wanted to have named joins, but I don't remember it.

I think one reason for a table object was so this:

itsdb.select_rows(('parse:i-id', 'result:mrs'), profile.join('parse', 'result'))

could be this:

profile.join('parse', 'result').select(('parse:i-id', 'result:mrs'))

But also maybe so I could join more than two tables:

table = profile['item'].join('parse').join('result')
table.select(('item:i-input', 'result:mrs'))

While the proposed behavior above seems useful, I will in any case not prioritize this at the moment.