Add helper to generate coverage report from CLI and IDE

coverage.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+pub get
+pub global activate coverage
+dart --pause-isolates-on-exit --enable-vm-service=8111 test/test_all.dart & sleep 5
+pub global run coverage:collect_coverage --port=8111 -o coverage.json --resume-isolates
+pub global run coverage:format_coverage --packages=.packages -i coverage.json -o coverage.lcov --lcov --report-on=lib/
+genhtml coverage.lcov --title "coverage report" --output-directory coverage_report
+open coverage_report/index.html