Bind number values using sqlite3 number bindings

This updates the plugin so that it binds number values using the
appropritate sqlite3 number binding functions (e.g. sqlite3_bind_int,
sqlite3_bind_double, etc.).

This fixes the issue where columns without a type affinity would store
number values as strings. The plugin now mirrors the behavior of the
HTML5 Web SQL API and stores the data as is.

Includes unit tests.