Add custom file format for simplecov coverage type (#2)

Most of the repos I checked use this format for coverage files.
Which is something between the legacy and new version.
The main differences that this format has:
 - there is no metadata fields;
 - it contains high level name, which can be configured by the users;
 - it uses lines and branches primitives (same as the new version).

Add custom file format for simplecov coverage type (#2)

Most of the repos I checked use this format for coverage files.
Which is something between the legacy and new version.
The main differences that this format has:
 - there is no metadata fields;
 - it contains high level name, which can be configured by the users;
 - it uses lines and branches primitives (same as the new version).