To facilitate rapid experimentation with SQL queries, add a shell to run commands and display results.

Attached is minimal proof-of-concept modeled loosely on the Linux sqlite3 REPL.  Here's a sample session:

    SQLite version 2.6.0

     Enter "help" for usage hints

    sqlite> open Irises.db
    sqlite> select distinct species from irises
    ('Iris-setosa',)
    ('Iris-versicolor',)
    ('Iris-virginica',)
    sqlite> select species, avg(pet_len), avg(sep_len) from irises group by species
    ('Iris-setosa', 1.464, 5.005999999999999)
    ('Iris-versicolor', 4.26, 5.936)
    ('Iris-virginica', 5.552, 6.587999999999998)
    sqlite> select count(*) from irises
    (150,)
    sqlite> quit