Add EIP712TypedData support

[hewigovens]

Reference:

• https://github.com/ethereum/EIPs/blob/master/EIPS/eip-712.md
• https://github.com/ethereum/EIPs/blob/master/assets/eip-712/Example.js

[hewigovens]

related PRs:

• EIP-712: Update assets to show array encoding ethereum/EIPs#1242
• EIP-712: Sign typed data MetaMask/metamask-extension#4803

[codecov-io]

Codecov Report

Merging #23 into master will increase coverage by 2.02%.
The diff coverage is 96.78%.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
+ Coverage   80.03%   82.05%   +2.02%     
==========================================
  Files          63       66       +3     
  Lines        2364     2675     +311     
==========================================
+ Hits         1892     2195     +303     
- Misses        472      480       +8

Impacted Files	Coverage Δ
...thereum/Solidity/EIP712/EIP712TypedDataTests.swift	100% <100%> (ø)
...ces/Ethereum/Solidity/EIP712/EIP712TypedData.swift	92.85% <92.85%> (ø)
Sources/Ethereum/Solidity/EIP712/GenericJSON.swift	94.93% <94.93%> (ø)
Sources/Ethereum/Solidity/ABIValue.swift	73.01% <0%> (+0.79%)	⬆️
Sources/Ethereum/Solidity/ABIEncoder.swift	89.36% <0%> (+1.06%)	⬆️

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[alejandro-isaza]

Let's add some documentation comments and bring the test coverage up.

[alejandro-isaza]

Great!

[vikmeup]

@hewigovens what's the latest on this?

[hewigovens]

@vikmeup wait for two related PRs (Array type encoding, metamask support)

[vikmeup]

@hewigovens we could probably merge this one and then add those two that you mentioned?

[hewigovens]

@vikmeup sure, let's create an issue to track this