Support explicit table mappings

[Pi Lanningham]

Requiring the decoration of classes with an attribute is inconvenient in some cases. An alternative, explicit mapping which bypasses the reflection to inspect the attributes would allow us to make use of this library in circumstances where we don't control the code for the objects we are saving.

[Pi Lanningham]

(I'll also be submitting a similar request to sql-lite.net)

[Martin Kuckert]

Have you created an issue against sqlite-net? Do you have a link?