Improve tests, save outputs of tests to temp file for better viewing …

[freewind]

…when test fails

Now if there is any test fails, it will show error messages like:

/Users/freewind/workspace/laser-ethereum/tests/testdata/inputs/returnvalue.sol: information of laser is changed, you can compare follow files to see the differences:
/Users/freewind/workspace/laser-ethereum/tests/testdata/outputs_expected/returnvalue.sol.json
/Users/freewind/workspace/laser-ethereum/tests/testdata/outputs_current/returnvalue.sol.json

We can compare the give two files to view the difference.

Some of the tests are still failing now, but you can see they are may be expected changes. So you can copy the files from outputs_current to outputs_expected and commit them, which is addressed in README_DEV.md too

[freewind]

@b-mueller If you think this solution is good enough, I can apply it to mythril too

[muellerberndt]

Yep, that works.