Add NvimTreeResize to resize the NvimTree window (#497)

doc/nvim-tree-lua.txt

@@ -49,6 +49,11 @@ It will also open the leafs of the tree leading to the file in the buffer
 
 Print clipboard content for both cut and copy
 
+|:NvimTreeResize|			          *:NvimTreeResize*
+
+Resize the NvimTree window to the given size. Example: `:NvimTreeresize 50`
+resizes the window to the width of 50.
+
 ==============================================================================
 OPTIONS				                  *nvim-tree-options*
 

lua/nvim-tree.lua

@@ -158,6 +158,11 @@ function M.find_file(with_open)
   lib.set_index_and_redraw(filepath)
 end
 
+function M.resize(size)
+  view.View.width = size
+  view.resize()
+end
+
 function M.on_leave()
   vim.defer_fn(function()
     if not view.win_open() then

plugin/tree.vim

@@ -40,6 +40,7 @@ command! NvimTreeToggle lua require'nvim-tree'.toggle()
 command! NvimTreeRefresh lua require'nvim-tree'.refresh()
 command! NvimTreeClipboard lua require'nvim-tree'.print_clipboard()
 command! NvimTreeFindFile lua require'nvim-tree'.find_file(true)
+command! -nargs=1 NvimTreeResize lua require'nvim-tree'.resize(<args>)
 
 let &cpo = s:save_cpo
 unlet s:save_cpo