Display average coverage in log

[mininny]

Addresses this issue.

It now adds the average coverage value of the report at the end of the coverage report to the console.

As-is

+---------------------+--------+
|     xcov Coverage Report     |
+---------------------+--------+
| A.framework               | 12.34% |
| B.framework               | 56.78% |
+---------------------+--------+

To-be

+---------------------+--------+
|     xcov Coverage Report     |
+---------------------+--------+
| A.framework               | 12.34% |
| B.framework               | 56.78% |
| Average Coverage     | xx.yy%  |
+---------------------+--------+

[joshdholtz]

I like this feature! Thank you for the contribution ❤️