Coverage stats improvements

[alexsaveliev]

• when calculating number of lines of code, stripping everything except idents. I think that line of code that contains no idents probably cannot be indexed - there is nothing to extract from. Examples may be: literals, comments
• separating uncovered and undiscovered files. "Undiscovered" file is a file that matches code file by extension but not listed in the discovered source units. "Uncovered" file was discovered during the scan phase but its coverage density is too small

[beyang]

1 comment, otherwise LGTM1