feat: Add commit count for ahead/behind symbols (#247)

Add logic for the git status module to display the number of commits the index is ahead or behind next to the symbol.

tests/testsuite/main.rs

@@ -3,6 +3,7 @@ mod cmd_duration;
 mod common;
 mod configuration;
 mod directory;
+mod git_status;
 mod golang;
 mod jobs;
 mod line_break;