Fix issue when file names contain invalid characters

[zorone]

This problem mostly occur when pulling file from Android to Windows.

I have to implement it in various spots.

1. check if source and destination from user argument is valid.
2. change module from os.path to posixpath referring from here, to prevent converting file name from '\\' to '/' on Android side.
3. convert file name in Local side to a valid one.

I also add --no-del option, which will prevent from removing files. I find it useful if I want to transferring to just one side. I implement it in various locations too.

1. change action variable to argparse.BooleanOptionalAction. Reference here.
2. Make sure that files won't get overridden if --no-del is set.
3. Set condition to not perform delete operation.

Lastly, I also tweak logging_fatal() a bit since it prevents program from running further when there are any fatal error occurs. In my opinion, it feels really bad when program stops while it could still proceed. Like when there are some bad file names. It will halt the works although you could just skip those bad ones.

I have put TODO and FIXME all over the places, you could remove it if you want.

[zorone]

@jb2170 Could you review my code, please? It's my first time I commit full work to an open source project. I'm scared I would mess up something.

[jb2170]

I'll have a look at this soon thanks! I'm a bit busy right now, but this project isn't orphaned.

(>19th August)

[zorone]

Sure!