Introduce cdk-sql-common

The primary purpose of this new crate is to have a common and shared codebase
for all SQL storage systems. It would force us to write standard SQL using best
practices for all databases.

This crate has been extracted from #878

crates/cdk-sql-common/src/lib.rs

@@ -0,0 +1,23 @@
+//! SQLite storage backend for cdk
+
+#![warn(missing_docs)]
+#![warn(rustdoc::bare_urls)]
+
+mod common;
+pub mod database;
+mod macros;
+pub mod pool;
+pub mod stmt;
+pub mod value;
+
+pub use cdk_common::database::ConversionError;
+
+#[cfg(feature = "mint")]
+pub mod mint;
+#[cfg(feature = "wallet")]
+pub mod wallet;
+
+#[cfg(feature = "mint")]
+pub use mint::SQLMintDatabase;
+#[cfg(feature = "wallet")]
+pub use wallet::SQLWalletDatabase;