feat(statistics): display some stats in the logs (#337)

* test: add more coverage

* docs: reorder and enhance typo

* docs(contributing): add more information about the npm scripts

* feat(statistics): add simple statistics

* feat(statistics): add more stats

* refactor(issues-processor): remove some options from the constructor

it should have been only useful for the tests

* feat(statistics): add stats for new stale or undo stale issues

* chore(rebase): handle rebase conflicts

__tests__/constants/default-processor-options.ts

@@ -41,5 +41,6 @@ export const DefaultProcessorOptions: IIssuesProcessorOptions = Object.freeze({
   exemptPrAssignees: '',
   exemptAllAssignees: false,
   exemptAllIssueAssignees: undefined,
-  exemptAllPrAssignees: undefined
+  exemptAllPrAssignees: undefined,
+  enableStatistics: false
 });