Proposal: add --bind flag to specify listen address

[110y]

What

• Add --bind flag to allow us to change listen address from localhost

Why

I'm using mo on my Linux server and viewing Markdown files from another device like a laptop PC.
Since now mo always uses localhost to listen on, I need to use some kind of reverse port forwarding technique like SSH options to connect to the remote mo server.
This works fine on a PC, but regarding a mobile device like iPhone, it's difficult to use this technique.
If mo allows us to change its binding address from localhost, we can connect to mo from other devices like a mobile device (via some kind of VPN like Tailscale to connect to servers).

I know my use case is bit tricky, but other Markdown viewer like markserv or madness also allow us to change the address.

@k1LoW I appreciate if you could take a look at this proposal, thanks!

[k1LoW]

@110y Thank you!!
I think this is an excellent feature!
However, due to the API specifications of mo, this will expose potentially dangerous APIs.
After merging this PR, I'll add a clear Notice ( or Warning ) message myself.

[110y]

@k1LoW

Thank you for accepting this PR! Now I'm reading Markdown files using mo even on my iPhone 📱

However, due to the API specifications of mo, this will expose potentially dangerous APIs.
After merging this PR, I'll add a clear Notice ( or Warning ) message myself.

Thank you for following up my PR! Regarding this point, I send another PR #103 to make us to be able to skip the confirmation.

I appreciate if you could take another look at the PR 🙏 (Please feel free to close the PR if it's not acceptable 🙏 )