added summary diagnostic modes

[AlexHaxe]

added markiscodecoverage.detailCoverageMode and markiscodecoverage.summaryWithCurly config parameters users can choose to have detailed diagnostics for all files (default == behaviour of previous versions), only for open files, only for active files or for no files. Files without detailed diagnostics show a single summary diagnostic message using a range from first uncovered line to last.

When using never for markiscodecoverage.detailCoverageMode, setting markiscodecoverage.summaryWithCurly = false will minimise curly underlining of uncovered code.