feat(#406): add set_icon_by_filetype (#407)

simply adds/updates user-defined filetypes to the internal filetypes
table.

fixes #406

Author: classabbyamp

README.md

@@ -166,7 +166,7 @@ You can override the default icon with the `set_default_icon(icon, color, cterm_
 require("nvim-web-devicons").set_default_icon('', '#6d8086', 65)
 ```
 
-### Getting icons by filetype
+### Getting and setting icons by filetype
 
 You can get the icon and colors associated with a filetype using the `by_filetype` functions:
 
@@ -177,6 +177,12 @@ require("nvim-web-devicons").get_icon_color_by_filetype(filetype, opts)
 require("nvim-web-devicons").get_icon_cterm_color_by_filetype(filetype, opts)
 ```
 
+or set the icon to use for a filetype with:
+
+```lua
+require("nvim-web-devicons").set_icon_by_filetype { cpp = "c", pandoc = "md", }
+```
+
 These functions are the same as their counterparts without the `_by_filetype` suffix, but they take a filetype instead of a name/extension.
 
 You can also use `get_icon_name_by_filetype(filetype)` to get the icon name associated with the filetype.

lua/nvim-web-devicons.lua

@@ -510,6 +510,10 @@ function M.set_icon(user_icons)
   end
 end
 
+function M.set_icon_by_filetype(user_filetypes)
+  filetypes = vim.tbl_extend("force", filetypes, user_filetypes or {})
+end
+
 function M.set_default_icon(icon, color, cterm_color)
   default_icon.icon = icon
   default_icon.color = color