Separate traverse directory into another goroutine

[wingyplus]

This commit move filepath.Walk into another goroutine to separate
layer between detect file changes and command execution. And separate
detect skip file/directory if file/folder has begin with dot.

[nattawitc]

I have 3 concerns about this.

• the absence of time.Sleep(800 * time.Millisecond) might make the goroutine that walkthrough file run too frequently and consume too much CPU.
• the default case in line 116 will keep the loop running without waiting for the actual change. this might consume CPU too.
• the stop case in main file exit program immediately without waiting for the goroutine to properly exit.

[wingyplus]

@nattawitc First and second points that you mentioned are fixed. For third point, I think it should add WaitGroup to wait it until exit.

[wingyplus]

All fixed

[nattawitc]

@AnuchitO thought?

[AnuchitO]

I agree it's a good idea. I also think about how to separate layer
the Watcher is responsible for a detect change and notifies whenever the file has changed.
the Commander is responsible for control flow
the Executor is responsible for executing and managing for the process
it just an idea right now.

For your pull request
"filepath.Walk into another goroutine to separate"

we might need it in the future when we have more trigger mechanism apart from File change (e.g. Interruption from a keyboard to force to rerun again). At the same time, by adding goroutine, while having the benefit of separating trigger and having the possibility to add multiple triggers, it also adds more complexity to the codebase and makes it harder to test

Right now, unit test of re very weak. I prefer to add more unittest first. before we add more complexity even though it looks trivial.

"And separate detect skip file/directory if file/folder has begin with a dot."

This is a good idea and very make it testable. I will apply this logic.
So, In future we will ignore watching the files that match patterns defined in .gitignore.

I very appreciate your contribution.
I will apply coding style from your pull request as well e.g. StopWalk, SkipFile error.
That add more readability into codebase.

[wingyplus]

I think we already have a conclusion. So close this PR.