Solidity: Improve test coverage of the Scanner

[axic]

libsolidity/parsing/Scanner.cpp has a test coverage of 69% when running the syntax tests, but 92% when also running the semantics (end-to-end) tests.

Should add test cases to the tes/solidity/syntaxTests directory.

Missing cases:

• unicode escapes
• upper case hex values
• multiline comments
• Token::Dec, Token::AssignSub, Token::AssignBitOr

[chriseth]

@herrBez thanks that you want to help out! Please create a pull request early so that we have a place for discussion. I'm not too much into how to extract coverage information either, but I think you have to compile with cmake -DCOVERAGE=ON ..; make and then use the codecov tool. If we are lucky, you will get coverage results on the pull request itself (but sometimes they are broken).

[herrBez]

Thank you very much for the support. I will try to conclude (hopefully soon!) (I am currently using codecov on my fork to see the test coverage). It is ok to make multiple commits or it is better a single commit with the fix for this issue?

[chriseth]

Feel free to do it in whatever way you like. At the end, depending on the amount of changes, a single commit is probably best, but it can always be squashed.