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.

[codecov-commenter]

Codecov Report

Merging #664 (8d5add2) into master (67b711d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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

Impacted Files	Coverage Δ
lib/api.js	100.00% <100.00%> (ø)
plugins/resources/plugin.utils.js	97.64% <100.00%> (ø)
plugins/truffle.plugin.js	100.00% <100.00%> (ø)

---

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 67b711d...8d5add2. Read the comment docs.

[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!