Implement revert

[cburgdorf]

What was wrong?

We need to have support for revert expressions.

How was it fixed?

1. Refactored test_function into two functions in order to re-use it for revert assertion
2. Mapped revert to revert(0,0) in YUL (Ignoring revert reasons Implement revert reasons #75 for now)
3. Added a contract test for revert
4. Added coverage for revert in the spec

To-Do

• Update Spec
• Clean up commit history

[codecov-commenter]

Codecov Report

Merging #74 into master will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   88.02%   87.90%   -0.13%     
==========================================
  Files          36       36              
  Lines        2279     2281       +2     
==========================================
- Hits         2006     2005       -1     
- Misses        273      276       +3     

Impacted Files	Coverage Δ
compiler/src/yul/mappers/functions.rs	0.00% <0.00%> (ø)
semantics/src/traversal/functions.rs	88.09% <0.00%> (-2.15%)	⬇️
compiler/src/abi/elements.rs	89.47% <0.00%> (-1.76%)	⬇️

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[codecov-io]

Codecov Report

Merging #74 into master will decrease coverage by 0.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   88.02%   87.94%   -0.08%     
==========================================
  Files          36       36              
  Lines        2279     2281       +2     
==========================================
  Hits         2006     2006              
- Misses        273      275       +2     

Impacted Files	Coverage Δ
compiler/src/yul/mappers/functions.rs	0.00% <0.00%> (ø)
semantics/src/traversal/functions.rs	88.09% <0.00%> (-2.15%)	⬇️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[g-r-a-n-t]

Code looks good. Just a few things in the spec that should be improved, mainly that we're referring to revert as an expression when it is considered to be a statement.