Allow multiple statement per invocation

[dnicolodi]

Currently a statement can be read from the standard input or passed as arguments. However, only one statement per command invocation is supported. Allow multiple statements, including interleaving BQL statements and shell commands. Allow to read statements to be executed from a file. BQL commands should be terminated by a semicolon. Shell commands are prefixed by a dot and terminated by newline. See what the sqlite3 shell does.

It would be nice to keep not requiring a semicolon to terminate BQL commands in the interactive shell, but it may be tricky.