Add nvim-tree filetype and re-apply colorscheme on sourcing init.vim

[akinsho]

Firstly thanks for the awesome plugin, it's super snappy 💯

Sorry I bundled two issues in one.

1. Buffer Filetypes

I noticed that the plugin doesn't give the nvim-tree buffers specific filetypes so it's hard to set autocommands or use the filetype to do whatever a user might want with that buffer e.g. nerdtree or coc-explorer etc. buffers have a filetype so I could have line number on or off by setting a filetype autocommand or using a ftplugin file. Or in my statusline I can check the filetype and show a formatted name with an icon for that kind of buffer or hide the statusline in that buffer altogether 🤷.

I'd be up for raising a PR for that if that interests you at all?

2. Buffer highlights disappear on sourcing init.vim

This is a fairly common issue with a lot of different plugins, as far as I can guess the highlights set in the nvim-tree buffer are only done once not on Colorscheme changed. Think a fix here would be register a function in the plugin to apply the highlights and call it when the colorscheme changes.

[kyazdani42]

Hi ! thanks for the kind words.
I'll make a PR when i have some time later today.

[kyazdani42]

also i have another issue with colors, i might also fix that in the same PR (colors do not apply properly for some colorschemes that don't set the nvim_color_x variables)