feat: add stake program methods; refactor instruction type handling

web3.js/src/sysvar.js

@@ -0,0 +1,18 @@
+// @flow
+import {PublicKey} from './publickey';
+
+export const SYSVAR_CLOCK_PUBKEY = new PublicKey(
+  'SysvarC1ock11111111111111111111111111111111',
+);
+
+export const SYSVAR_RENT_PUBKEY = new PublicKey(
+  'SysvarRent111111111111111111111111111111111',
+);
+
+export const SYSVAR_REWARDS_PUBKEY = new PublicKey(
+  'SysvarRewards111111111111111111111111111111',
+);
+
+export const SYSVAR_STAKE_HISTORY_PUBKEY = new PublicKey(
+  'SysvarStakeHistory1111111111111111111111111',
+);