Fix highlight for atoms containing @ character

Author: William Sanches

Diff for: spec/syntax/atom_spec.rb

@@ -88,4 +88,19 @@ def project do
     end
     EOF
   end
+
+  it 'detects atoms containing @ in it' do
+    expect(<<~EOF).to include_elixir_syntax('elixirAtom', '@somewhere')
+      :atom@somewhere
+    EOF
+    expect(<<~EOF).to include_elixir_syntax('elixirAtom', '@somewhere')
+      [atom@somewhere: nil]
+    EOF
+  end
+
+  it 'detects atoms containing Unicode letters in it' do
+    expect(<<~EOF).to include_elixir_syntax('elixirAtom', 'ó')
+      :atóm
+    EOF
+  end
 end

Diff for: syntax/elixir.vim

@@ -41,9 +41,9 @@ syn match   elixirOperator '\\\\\|::\|\*\|/\|\~\~\~\|@'
 
 syn match   elixirAlias '\([a-z]\)\@<![A-Z]\w*\%(\.[A-Z]\w*\)*'
 
-syn match   elixirAtom '\(:\)\@<!:\%([a-zA-Z_]\w*\%([?!]\|=[>=]\@!\)\?\|<>\|===\?\|>=\?\|<=\?\)'
+syn match   elixirAtom '\(:\)\@<!:\%([a-zA-Z_]\%(\w\|@\|\P\)*\%([?!]\|=[>=]\@!\)\?\|<>\|===\?\|>=\?\|<=\?\)'
 syn match   elixirAtom '\(:\)\@<!:\%(<=>\|&&\?\|%\(()\|\[\]\|{}\)\|++\?\|--\?\|||\?\|!\|//\|[%&`/|]\)'
-syn match   elixirAtom "\%([a-zA-Z_]\w*[?!]\?\):\(:\)\@!"
+syn match   elixirAtom "\%([a-zA-Z_]\%(\w\|@\|\P\)*[?!]\?\):\(:\)\@!"
 
 syn keyword elixirBoolean true false nil