token-sale

After following the excellent tutorial given by Gregory from http://www.dappuniversity.com (github link: https://github.com/dappuniversity/dapp_token) through his Youtube video series (https://www.youtube.com/channel/UCY0xL8V6NzzFcwzHCgB8orQ), I updated the code in a few ways:

1. made compatible with solidity version 5.0 (constructor, added the emit keyword, address(this) for the contract address)
2. Integrated SafeMath
3. Cleaned up promises in testing to use async/await
4. Used the truffle-assertions library (https://www.npmjs.com/package/truffle-assertions) to handle reverts and events
5. Added a beforeEach statement in the contract testing so that contract instance code would be implemented once