* Update ReentrancyGuard for Istanbul Hard Fork

Changes:
Added L37, `_guardCounter = 1;`

Rationale:
The planned _Istanbul Hard Fork_ will implement [EIP 2200](https://github.com/ethereum/EIPs/blob/e4d4ea348e06c54d0075c400dc7b72430d427ff1/EIPS/eip-2200.md), which implements "net gas metering" for `sstore` operations. If the final value of `_guardCounter` is unchanged relative to the original value of it, a gas refund will be applied and charges for changing the value of `_guardCounter` will effectively not exist. This ends up being cheaper than the current implementation ONLY AFTER Istanbul. Before Istanbul, the added line actually ends up costing more gas.

Note that if `_guardCounter` is `0` initially, the initial cost and subsequent refund will both be larger than if `_guardCounter` is `1` initially. Although in both cases, the net gas cost (`gasCost - gasRefund`) are equal, it's better in terms of cost to have both the gas cost and refund smaller, as there is some limit to the percentage of a gas refund that can actually be realized.

* Update CHANGELOG.md

Added note for change to ReentrancyGuard.sol

* Update ReentrancyGuard.sol

* Update CHANGELOG.md

Bumps [ethereumjs-util](https://github.com/ethereumjs/ethereumjs-util) from 6.1.0 to 6.2.0.
- [Release notes](https://github.com/ethereumjs/ethereumjs-util/releases)
- [Changelog](https://github.com/ethereumjs/ethereumjs-util/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ethereumjs/ethereumjs-util/compare/v6.1.0...v6.2.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps solidity-docgen from 0.3.9 to 0.3.11.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [truffle](https://github.com/trufflesuite/truffle) from 5.0.42 to 5.0.44.
- [Release notes](https://github.com/trufflesuite/truffle/releases)
- [Commits](https://github.com/trufflesuite/truffle/compare/truffle@5.0.42...truffle@5.0.44)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

"standard also bring" -> "standard also brings"
"killer feature are" -> "killer feature is"

* add how to upgrade from 2.4-beta

* add how-to

* Update CHANGELOG.md

(cherry picked from commit bddbbe99)

(cherry picked from commit 2d304153)

(cherry picked from commit 9113335c)

(cherry picked from commit 76a1d7a3)

* Add withdrawWithGas

* Improve docs

* Add changelog entry

* Update contracts/payment/PullPayment.sol

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

* Remove repeated comment

* Update changelog entry

* Fix inline docs

* Fix changelog formatting

(cherry picked from commit d6e10ab7)

(cherry picked from commit eaee98f2)

Fixed:
-DetailedERC20 in the constructor
-minters should be _minters
-New example instead of rename function

(cherry picked from commit 5c8fa0f0)

(cherry picked from commit fcd77a4a)

(cherry picked from commit 5702a844)

* Add Address.sendEther

* Add documentation to sendEther

* Add changelog entry

* Rename sendEther to sendValue

(cherry picked from commit 8d166f3e)

* Merge GSNBouncerBase into GSNRecipient

* Remove emtpy implementations for _pre and _post

* Rename bouncers to recipients

* Rename bouncers documentation to strategies

* Rewrite guides and docstrings to use the strategy naming scheme

* Address review comments

* Apply suggestions from code review

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

* change wording of docs

(cherry picked from commit aae95db4)

* Improve PullPayment docs

* Reword escrow note

* Update contracts/payment/PullPayment.sol

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>
(cherry picked from commit 9e19d90c)

(cherry picked from commit 53f1b116)

(cherry picked from commit 13b85c68)

(cherry picked from commit eda29e06)

* switch index to show arg names

* add index separators

* add classes to style variable type and name

* add class for inherited part of index

* use inheritedItems in contracts template

* refactor template to use explicit if and each

(cherry picked from commit 5d6a040f)

(cherry picked from commit e557a54c)

(cherry picked from commit 77ae18f1)

(cherry picked from commit c8665228)