Updated Formatter for better metrics

[shetty-tejas]

Re-opened the previous PR: #7.

---

I was making a Github Actions project for working with SimpleCov. Turns out this being the recommended gem by SimpleCov, didn't have some functionalities I was thinking of adding support for. So added it here in this PR. If you have any thoughts or suggestions do let me know 😄

What's Changed:

• Minimum Coverage Check for file. If fails, the file name and the percent_covered is collected in errors.
• Groups now contain more information such as covered_lines, missed_lines and total_lines.
• Also returns config details like minimum_coverage and minimum_coverage_by_file.
• Total metrics as default (even when groups are not available).

[shetty-tejas]

@pboling @f-moya Any changes you guys would like me to integrate?

[pboling]

LGTM