Factored out "init_v8_flags", "init_logger" and
"get_subcommand" from "main" function.
Also "Worker" was removed in favor of moving
logic to "MainWorker" and "WebWorker" respectively.
This commit moves following tools into a single "tools"
module located at "cli/tools/mod.rs":
- formatter
- linter
- test runner
- coverage collector
- installer
- binary upgrader
- repl