feat: allow exclude by buftypes

[ofseed]

Close #72

There are too many file types that need to be ignored, there are file types I ignored:

https://github.com/ofseed/nvim/blob/f3388dd77834c2d361e03296afbf617a86b147a4/lua/plugins/ui/marks.lua#L21-L48

But if we can ignore it by buftypes, that would be much easier, I only need to ignore nofile buftype.

[ofseed]

What made me create this PR is, in neovim, floating windows do not respect the signcolumn users set, they must be signcolumn=auto by default, which causes marks.nvim place signs in these floating windows. For some floating windows with a common filetype like markdown, it is not possible to ignore them by filetypes.

[chentoast]

LGTM. Thanks for the PR!