Pratyaksh Singh

This pull request is for the functions [onRootChange](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#onRootChange) and [removeRootChangeListener](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#removeRootChangeListener) given in issue number #41. The aim here is to call a callback every time the root is updated.

This pull request is for the functions onLogs and removeLogListener given in issue number #41. The main aim is to call a callback whenever logs are updated.

This pull request is in regards with issue number #90

Currently the web socket doesn't deal with error message received in subscription and also fails when un-subscription is done before the notification for successful subscription has been received.

This pull request implements the [onSlotChange](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#onSlotChange) and [removeSlotChangeListener](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#removeSlotChangeListener) function related to issue number https://github.com/mschneider/solcpp/issues/41. The goal here is to get notification every time a slot is changed.

This pr implements the functions [onSlotUpdate](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#onSlotUpdate) and [removeSlotUpdateListener](https://solana-labs.github.io/solana-web3.js/classes/Connection.html#removeSlotUpdateListener) associated with #41 The aim here is to get notification whenever any of the slot is updated.