Add -w option for watching files

[rniii]

Pretty rudimentary for now. Could have been done with watchexec, but I think its useful as a builtin feature.

Example dev task:

### dev

```sh
maid -w src build &
maid -w src -w public serve &
wait
```

TODO

• Ignoring file patterns
• Handle .gitignore etc
• Option to restart process instead of waiting

[rniii]

The Windows build is already a bit of a large size, so I'm curious if this makes it worse. -split-objs doesn't work on it, so only entire libraries are linked with it, but I think most of it might be base alone

[rniii]

Hm, strip seems to reduce it to 18mb, and upx reduces it further to a more reasonable 4mb

[rniii]

-r is randomly getting stuck on a loop now