Syntax: Add elm module group

Why
---

I want to be able to differentiate Elm modules from Elm types

How
---

* Create `elmModule` highlight group
* Link `elmModule` to `Type`, the group conventionally used for modules

syntax/elm.vim

@@ -8,7 +8,7 @@ endif
 syn keyword elmConditional else if of then
 syn keyword elmAlias alias
 syn keyword elmTypedef contained type port
-syn keyword elmImport exposing as import module where
+syn keyword elmImport contained exposing as import module where
 
 " Operators
 syn match elmOperator contained "\([-!#$%`&\*\+./<=>\?@\\^|~:]\|\<_\>\)"
@@ -17,6 +17,10 @@ syn match elmOperator contained "\([-!#$%`&\*\+./<=>\?@\\^|~:]\|\<_\>\)"
 syn match elmType "\<[A-Z][0-9A-Za-z_'-]*"
 syn keyword elmNumberType number
 
+" Modules
+syn match elmModule "\<[A-Z][0-9A-Za-z_'-]*\."me=e-1
+syn match elmModule "^\(module\|import\)\s\+[A-Z][0-9A-Za-z_'-\.]*\(\s\+as\s\+[A-Z][0-9A-Za-z_'-\.]*\)\?\(\s\+exposing\)\?" contains=elmImport
+
 " Delimiters
 syn match elmDelimiter  "[,;]"
 syn match elmBraces  "[()[\]{}]"
@@ -73,6 +77,7 @@ hi def link elmAlias Delimiter
 hi def link elmOperator Operator
 hi def link elmType Identifier
 hi def link elmNumberType Identifier
+hi def link elmModule Type
 
 syn sync minlines=500