New documentation setup (#1708)

* initial docsite setup

* switch from pushd to cd

* install and set up solidity-docgen

* use the docsite branch next for now

* make it clear that env var is a repository

* add a clarifying comment about a relative path

* change relative to absolute path in docsite script

* add docgen script

* add first few READMEs for contract documentation

* update solidity-docgen

* add docsite as dependency and adjust script

* update openzeppelin-docsite

* update solidity-docgen

* remove dummy text

* update docgen and docsite

* update openzeppelin-docsite

* add netlify.toml

* udpate tokens guide for 2.2

* add DOCUMENTATION.md

* Update docs/learn-about-utilities.md

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

* fix PaymentSplitter docs wording

* update solidity-docgen

* add missing ERC20 contracts

* update solidity-docgen

* trigger deploy with cleared cache

* update solidity-docgen

* update openzeppelin-docsite

* remove travis docs setup

* update openzeppelin-docsite

* switch to published solidity-docgen

contracts/payment/PaymentSplitter.sol

@@ -5,7 +5,7 @@ import "../math/SafeMath.sol";
 /**
  * @title PaymentSplitter
  * @dev This contract allows to split Ether payments among a group of accounts. The sender does not need to be aware
- * that the Ether will be split in this way, since it is handled purely by the contract.
+ * that the Ether will be split in this way, since it is handled transparently by the contract.
  *
  * The split can be in equal parts or in any other arbitrary proportion. The way this is specified is by assigning each
  * account to a number of shares. Of all the Ether that this contract receives, each account will then be able to claim