Tilde/Home paths are incompatible with filename completion on windows

Issue

Tilde paths work on windows, but only using forward slash (/) separated paths.
Filename completion works on windows, but only using backslash (\) separated paths.
This means that autocomplete cannot be used with home-paths on windows, despite the machinery for both being implemented.

Examples

Assuming the file C:\Users\User\foo.txt exists, micro:

• correctly autocompletes C:\Users\User\foo to C:\Users\User\foo.txt
• fails to autocomplete C:/Users/User/foo
• fails to autocomplete ~\foo
• fails to autocomplete ~/foo

In addition:

• micro fails to open ~\foo.txt (seemingly attempting to find some user \foo.txt)
• it does, however, successfully open ~/foo.txt

Proposed Solution:

Update homeString := strings.Split(path, "/")[0] in util.go to use string(os.PathSeparator) instead of "/", as is already the case in autocomplete.go (or vice versa), or otherwise come up with some solution to make both forward and backslashes work in both places on windows.

Start in internal/util/util.go at the homeString path handling and compare it with the separator logic in internal/buffer/autocomplete.go. Reproduce the listed Windows completion and opening cases, then verify that both forward- and backslash-separated home paths work consistently.