feat: add elixir support (#148)

Add support for Elixir, Embedded Elixir, and HEEx filetypes

- Elixir comments are same as Ruby
- Embedded Elixir and HEEx are same as HTML

Author: sbennett33

lua/Comment/ft.lua

@@ -30,6 +30,8 @@ local L = {
     css = { M.cxx_b, M.cxx_b },
     dhall = { M.dash, M.haskell_b },
     dot = { M.cxx_l, M.cxx_b },
+    eelixir = { M.html, M.html },
+    elixir = { M.hash },
     elm = { M.dash, M.haskell_b },
     fennel = { M.lisp_l },
     fish = { M.hash },
@@ -40,6 +42,7 @@ local L = {
     graphql = { M.hash },
     groovy = { M.cxx_l, M.cxx_b },
     haskell = { M.dash, M.haskell_b },
+    heex = { M.html, M.html },
     html = { M.html, M.html },
     htmldjango = { M.html, M.html },
     idris = { M.dash, M.haskell_b },