Add support for COUNT(*)

One approach would be to make this a 0-arg function, but that ends up being hard
because we don't know the input number of rows (only the output number of rows),
so instead, I just parse it into COUNT(1), which is equivalent.
Implement SELECT *

We parse * into its own special select field, and before compiling select fields
(but after compiling the table expression), we look for any stars and expand
them into uncompiled select fields based on whether we're selecting from a JOIN
or not.

This also fixes a bug in JOIN evaluation where the table component of columns
was being ignored when constructing the data.