[REQUEST] Skunk Score should be a "GPA score"-like letter based on a 0-100 scale

**Before we start...:**

- [x] I checked the documentation and didn't find this feature
- [x] I checked to make sure that this feature has not already been requested

**Branch/Commit:**

`main` branch.

**Describe the feature:**

> **As a new user**
> **I want to run `skunk`**
> **So that I can see a list of GPA scores per file**

**Problem:**

> **As a new user**
> **I run `skunk`**
> **And then I see a list of skunk scores**
> **And I don't understand if my app is in great shape or horrible shape**

**Current:**

```
+-----------------------------------------------------+----------------------------+----------------------------+----------------------------+----------------------------+----------------------------+
| file | skunk_score | churn_times_cost | churn | cost | coverage |
+-----------------------------------------------------+----------------------------+----------------------------+----------------------------+----------------------------+----------------------------+
| lib/skunk/cli/commands/default.rb | 166.44 | 1.6643999999999999 | 3 | 0.5548 | 0 |
| lib/skunk/cli/application.rb | 139.2 | 1.392 | 3 | 0.46399999999999997 | 0 |
| lib/skunk/cli/command_factory.rb | 97.6 | 0.976 | 2 | 0.488 | 0 |
| test/test_helper.rb | 75.2 | 0.752 | 2 | 0.376 | 0 |
| lib/skunk/rubycritic/analysed_module.rb | 48.12 | 1.7184 | 2 | 0.8592 | 72.72727272727273 |
| test/lib/skunk/cli/commands/status_reporter_test.rb | 45.6 | 0.456 | 1 | 0.456 | 0 |
| lib/skunk/cli/commands/base.rb | 29.52 | 0.2952 | 3 | 0.0984 | 0 |
| lib/skunk/cli/commands/status_reporter.rb | 8.0 | 7.9956 | 3 | 2.6652 | 100.0 |
| test/lib/skunk/rubycritic/analysed_module_test.rb | 2.63 | 2.6312 | 2 | 1.3156 | 100.0 |
| lib/skunk.rb | 0.0 | 0.0 | 2 | 0.0 | 0 |
| lib/skunk/cli/options.rb | 0.0 | 0.0 | 2 | 0.0 | 0 |
| lib/skunk/version.rb | 0.0 | 0.0 | 2 | 0.0 | 0 |
| lib/skunk/cli/commands/help.rb | 0.0 | 0.0 | 2 | 0.0 | 0 |
+-----------------------------------------------------+----------------------------+----------------------------+----------------------------+----------------------------+----------------------------+
```

**Proposed:**

```
+-----------------------------------------------------+----------------------------+----------------------------+----------------------------+----------------------------+----------------------------+
| file | skunk_score | churn_times_cost | churn | cost | coverage |
+-----------------------------------------------------+----------------------------+----------------------------+----------------------------+----------------------------+----------------------------+
| lib/skunk/cli/commands/default.rb | F (7/100) | 1.6643999999999999 | 3 | 0.5548 | 0 |
| lib/skunk/cli/application.rb | D (47/100) | 1.392 | 3 | 0.46399999999999997 | 0 |
| lib/skunk/cli/command_factory.rb | A (93/100) | 0.976 | 2 | 0.488 | 0 |
```

**I will abide by the [code of conduct](https://github.com/fastruby/skunk/blob/main/CODE_OF_CONDUCT.md)**