Version to 0.4.1 for sqlite-bundled

Fixes Electron100#7

Implement Serialize/Deserialize for Many

Requires allowing a table name in a Query to be a Cow instead of
always a &'static str, hence the bump to 0.4

Add unqiue constraint for model fields

May be specified by adding #[unique] to a field

Remove separate IntoSql trait

into_sql method now optional on ToSql trait

Update versions for 0.2.1

Add category

Publish butane cli