RFR: New JDK coverage reports, refactoring

[Alexandre Iline]

File items. Which could be anything of which there is a set per file, for example, methods, fields.
Command line API.
UnchangedCodeFilter
More coverage comparison reports.
More JDK reports, JDK reports moved to a sub-package. More refactoring
Tests

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Commit messages:
 - trailing space
 - formatting, comments
 - File items. Which could be anything of which there is a set per file, for example, methods, fields.

Changes: https://git.openjdk.org/jcov/pull/56/files
  Webrev: https://webrevs.openjdk.org/?repo=jcov&pr=56&range=00
  Stats: 4033 lines in 42 files changed: 3673 ins; 236 del; 124 mod
  Patch: https://git.openjdk.org/jcov/pull/56.diff
  Fetch: git fetch https://git.openjdk.org/jcov.git pull/56/head:pull/56

PR: https://git.openjdk.org/jcov/pull/56