[database] Add AnyDatabase and ConfigurableDatabase

This is related to #43

src/database/memory.rs

@@ -34,7 +34,7 @@ use bitcoin::consensus::encode::{deserialize, serialize};
 use bitcoin::hash_types::Txid;
 use bitcoin::{OutPoint, Script, Transaction};
 
-use crate::database::{BatchDatabase, BatchOperations, Database};
+use crate::database::{BatchDatabase, BatchOperations, ConfigurableDatabase, Database};
 use crate::error::Error;
 use crate::types::*;
 
@@ -450,6 +450,14 @@ impl BatchDatabase for MemoryDatabase {
     }
 }
 
+impl ConfigurableDatabase for MemoryDatabase {
+    type Config = ();
+
+    fn from_config(_config: &Self::Config) -> Result<Self, Error> {
+        Ok(MemoryDatabase::default())
+    }
+}
+
 #[cfg(test)]
 impl MemoryDatabase {
     // Artificially insert a tx in the database, as if we had found it with a `sync`