Sqlite open function to allow connection to a sqlite file

[alaingilbert]

This pull request allow you to actually open a connection to a sqlite file.

In the current state, you can only open a in-memory database.

Example:

use toasty_sqlite::Sqlite;
// ...
let driver = Sqlite::open("my_database.db").unwrap();

[codegod100]

See also #9. At least people want to see the same features

[carllerche]

I merged #9 already, but I think Sqlite::open probably is a better name. Feel free to open a new PR that renames the method to open.