* Added basic Escrow
* PullPayment now uses an Escrow, removing all trust from the contract
* Abstracted the Escrow tests to a behaviour
* Added ConditionalEscrow
* Added RefundableEscrow.
* RefundableCrowdsale now uses a RefundEscrow, removed RefundVault.
* Renaming after code review.
* Added log test helper.
* Now allowing empty deposits and withdrawals.
* Style fixes.
* Minor review comments.
* Add Deposited and Withdrawn events, removed Refunded
* The base Escrow is now Ownable, users of it (owners) must provide methods to access it.
* fix: clean up solium linting errors
* fix: make various contracts natspec compliant
* fix: this.balance deprecated; convert to address(this).balance
* fix: contract.call deprecated and switch to gasleft()
* fix: ignore empty block rule project-wide
* fix: add ignore cases for the rest of the linting warnings
* Update to ganache-cli v6.1.0 and truffle v4.1.0
* Update to stable version of ganache-cli
* fix: update event emission warning
- Fix event emission warnings for solidity 4.21 after truffle has been
updated to use this version
* fix pr review comments
* update to truffle v4.1.5
* update package-lock
* add additional emit keywords
* update solidity-coverage to 0.4.15
* update to solium 1.1.6
* fix MerkleProof coverage analysis by testing through wrapper
* change version pragma to ^0.4.21
* fix solium linting errors
