Easier API for custom column selection

[petamaj]

Couple observations:

1. make the default method names the shortest
2. don't decouple column selection (currently via Select! macro) with header name specification (arg to function)
3. if possible, update the macro, or move to a different mechanism so that code completion works on the attributes

[kondziu]

Note from the discussion: db.projects().select(columns!(project::Id, project::URL))

[petamaj]

Another note from the discussion anfter realizing that select! and columns! will both be size limited:

.select( vec![(DSLDude, "name"), (DSLDude, "name")])

[petamaj]

And maybe having the names of the attributes and the names of rust functions that get them be the same ;-D