Move Bank to its own crate

Also:
* counters.rs to solana_metrics
* genesis_block.rs to solana_sdk

sdk/src/timing.rs

@@ -9,6 +9,14 @@ pub const NUM_TICKS_PER_SECOND: usize = 10;
 pub const DEFAULT_TICKS_PER_SLOT: u64 = 8;
 pub const DEFAULT_SLOTS_PER_EPOCH: u64 = 64;
 
+/// The number of most recent `last_id` values that the bank will track the signatures
+/// of. Once the bank discards a `last_id`, it will reject any transactions that use
+/// that `last_id` in a transaction. Lowering this value reduces memory consumption,
+/// but requires clients to update its `last_id` more frequently. Raising the value
+/// lengthens the time a client must wait to be certain a missing transaction will
+/// not be processed by the network.
+pub const MAX_ENTRY_IDS: usize = NUM_TICKS_PER_SECOND * 120;
+
 pub fn duration_as_us(d: &Duration) -> u64 {
     (d.as_secs() * 1000 * 1000) + (u64::from(d.subsec_nanos()) / 1_000)
 }