Add Hardhat support

[cgewecke]

TODO

• Add HARDHAT_README.md (Add hardhat readme #567)
• Investigate & resolve coverage differences between Buidler & HH (Attach to Hardhat VM for trace #566)
  • ConvertLib (call) is 0 vs. 100
  • EtherRouter differences
• Use higher gas limits (because some people set their defaults at MAX) (Remove death for hh & raise gas to maximum  #565)
• Replace death (it's not working anymore) (Remove death for hh & raise gas to maximum  #565)
• Add tests for more complex compiler configs (Add complex compilation test case #563)
• Add hardhat-e2e (Use real Zeppelin (instead of fork) as E2E #557)
  • Run beta vs. synthetix 739 (Testing solidity-coverage hardhat plugin synthetix#2)
• buidler or hardhat conditional require entrypoint (for backwards compatibility) (Add shared buidler / hardhat plugin entrypoint #564)
  • Rename everything (Port Buidler tests to Hardhat #561)
  • Migrate most Buidler tests to hardhat (preserve a couple for old times) (Port Buidler tests to Hardhat #561)
• HardhatEVM hook (Split hardhat & builder / support HardhatEVM #560)
• HardhatPluginError (Port Buidler tests to Hardhat #561)
• Implement/investigate Allow configuring default sender account in Buidler plugin #552 (configurable default account) (Set network "from" / fix trace logic #562)
• Is Cannot keep mock contracts in test directory #467 fixed by this? Check and add test....

[codecov-io]

Codecov Report

Merging #548 (1dd9501) into master (6761556) will decrease coverage by 0.93%.
The diff coverage is 95.09%.

@@            Coverage Diff             @@
##           master     #548      +/-   ##
==========================================
- Coverage   99.27%   98.33%   -0.94%     
==========================================
  Files          20       22       +2     
  Lines         824      962     +138     
==========================================
+ Hits          818      946     +128     
- Misses          6       16      +10     

Impacted Files	Coverage Δ
plugins/resources/nomiclabs.ui.js	100.00% <ø> (ø)
plugins/resources/truffle.utils.js	100.00% <ø> (ø)
lib/collector.js	85.71% <57.14%> (-14.29%)	⬇️
lib/api.js	96.96% <71.42%> (-3.04%)	⬇️
plugins/nomiclabs.plugin.js	75.00% <75.00%> (ø)
plugins/hardhat.plugin.js	97.72% <97.72%> (ø)
plugins/buidler.plugin.js	100.00% <100.00%> (ø)
plugins/resources/nomiclabs.utils.js	100.00% <100.00%> (ø)
plugins/resources/plugin.utils.js	97.61% <100.00%> (+0.32%)	⬆️
plugins/truffle.plugin.js	100.00% <100.00%> (ø)
... and 3 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6761556...1dd9501. Read the comment docs.

[junderw]

Note: The README only refers to buidler. Perhaps it should also make mention of hardhat.

[cgewecke]

@junderw Ah yes, thanks.