Add new hook and make temporary contracts directory configurable

[rynobey]

This PR adds two small features:

• A new hook that gets called right before compiling the instrumented source code (onPreCompile)
• The ability to specify an alternative temporary directory to use for the instrumented source code

I have made an attempt to update the documentation and added the hook to the existing test - please let me know if I can add anything else to make the PR more complete.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.69%. Comparing base (67b711d) to head (8d5add2).
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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #664   +/-   ##
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  Coverage   98.68%   98.69%           
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  Files          22       22           
  Lines         991      993    +2     
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+ Hits          978      980    +2     
  Misses         13       13           

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[cgewecke]

This is great, thanks so much!

Would it be possible to add docs for the hook and the new temp contracts directory option to the config options table in the

• README.md
• HARDHAT_README.md

A brief sentence about how the preCompile hook is useful would also be nice.

(That table is a bit painful to add to in markdown, sorry about this...)

[cgewecke]

Fantastic, thanks again.

(Will hopefully publish this weekend)

[rynobey]

Hi @cgewecke, just wanted to follow up - I could be missing it but I don't see any new releases containing this work (yet)?

[cgewecke]

Hi! I'm so sorry. I thought I had published this, thanks for the ping.

I'need to add some tests for #667 tomorrow and will merge and publish then.

[rynobey]

Awesome :) Thanks!!

[cgewecke]

This is now published in 0.7.18

[rynobey]

Awesome!