better syntax for line continuations

Part of #4

syntax/fish.vim

@@ -8,20 +8,25 @@ syntax keyword fishRepeat while for
 syntax keyword fishLabel case
 
 syntax match fishComment /#.*/
+syntax match fishSpecial /\\$/
 syntax match fishIdentifier /\$[[:alnum:]_]\+/
 syntax region fishString start=/'/ skip=/\\'/ end=/'/
 syntax region fishString start=/"/ skip=/\\"/ end=/"/ contains=fishIdentifier
 syntax match fishCharacter /\v\\[abefnrtv *?~%#(){}\[\]<>&;"']|\\[xX][0-9a-f]{1,2}|\\o[0-7]{1,2}|\\u[0-9a-f]{1,4}|\\U[0-9a-f]{1,8}|\\c[a-z]/
-syntax match fishStatement /\v%(^|\(|;)\s*\zs\k+/
+syntax match fishStatement /\v;\s*\zs\k+>/
+syntax match fishCommandSub /\v\(\s*\zs\k+>/
+syntax region fishLineContinuation matchgroup=fishStatement start=/\v^\s*\zs\k+>/ skip=/\\$/ end=/$/ contains=fishSpecial,fishIdentifier,fishString,fishCharacter,fishStatement,fishCommandSub
 
 highlight! link fishKeyword Keyword
 highlight! link fishConditional Conditional
 highlight! link fishRepeat Repeat
 highlight! link fishLabel Label
 highlight! link fishComment Comment
+highlight! link fishSpecial Special
 highlight! link fishIdentifier Identifier
 highlight! link fishString String
 highlight! link fishCharacter Character
 highlight! link fishStatement Statement
+highlight! link fishCommandSub fishStatement
 
 let b:current_syntax = 'fish'