Misc scala utilities shared by the lichess.org scala projects.

• core provides scala library extensions, opaque type improvements, and low-level utilities.
• model has common types and relies on core opaque types.
• playJson extends JsValue and offers handlers for common types.
• lila contains higher-level utilities and relies on all of the above.

Projects using scalalib include:

• scalachess
• lila
• lila-ws
• lila-search
• lichess-db