Add .run command

.run executes semicolon-separated commands in a file, as opposed to
newline-separated commands like .read.

(Still trying to figure out how to write the tests for this... any hints?)

Closes #4
The idea to run the whole file as a single SQL script rather than treat contents as semi colon separated commands of 'sql-cli'; which is what 'read' already does. If we wanted to change the delimiter we could have a switch on read but that's not what we want since semi colon can also be inside a quoted string and simply splitting by semi colon would give incorrect sql.