message: Update vim syntax a bit
diff: @@ -20,13 +20,14 @@ endfunction
  " ---------------------------
  " --- Basic syntax groups ---
  " ---------------------------
  -"Keywords
  -syntax keyword brilMain main contained
  -
  " Identifiers
  -let identifierRegexp = '\a\w*'
  +let identifierRegexp = '(\a|_)\w*'
  call s:DefSynGroup('brilVariable', identifierRegexp, 'contained')
  +" Tokens
  +let funcRegexp = s:ConcatRegexp('\@', identifierRegexp)
  +call s:DefSynGroup('brilFuncName', funcRegexp, 'contained')
  +
  " Types
  " NOTE: this overlaps with identifiers, but is given higher precedence when declared afterwards.
  let typeRegexp = 'int|bool'
  @@ -90,8 +91,8 @@ call s:DefSynRegion('brilValueInstr', brilTypedVarRegexp, ';', 'oneline containe
  " --- Top Level Syntax Group ---
  " ------------------------------
  " Functions
  -let brilFunStartRegexp = s:ConcatRegexp(identifierRegexp, '\s*\{')
  -call s:DefSynRegion('brilFun', brilFunStartRegexp, '}', 'contains=brilComment,@brilValue,brilMain,brilValueInstr,brilBranchInstr,brilEffectInstr,brilLabel')
  +let brilFunStartRegexp = s:ConcatRegexp(funcRegexp, '\s*\{')
  +call s:DefSynRegion('brilFun', brilFunStartRegexp, '}', 'contains=brilComment,@brilValue,brilFuncName,brilValueInstr,brilBranchInstr,brilEffectInstr,brilLabel')
  "Infinite look-behind: not efficient, but probably ok for most people nowadays.
  syn sync fromstart
  @@ -102,7 +103,7 @@ syn sync fromstart
  highlight default link brilComment Comment
  highlight default link brilLabel Label
  highlight default link brilVariable Identifier
  -highlight default link brilMain Function
  +highlight default link brilFuncName Function
  highlight default link brilType Type
  highlight default link brilValueOp Operator
  highlight default link brilEffectOp Keyword
  