Update behaviour: swift Codable with Optional fields

[Alkenso]

In some past SQLiteEncoder skips to update the column if the Codable's optional field is nil
Seems after #838 it starts to place null if the value is nil, which is not convenient in some cases (often you want to update only part of the fields)

Please provide either

• example/docs how to update only non-nil fields
• additional Encoder setting that would configure this behaviour

[jberkel]

There wasn't really any change done as part of #838 (it looks like the issue was closed without resolving it).
The last changes to the codable functionality was done in #1138

[Alkenso]

And what do you think to add such flexibility to SQLiteEncoder? To give and option to encode nil and null with replacement / just ignore nils