Highlight multiline strings

[Alloyed]

Elm supports long strings ala python

"normal string"
"""loooong string"""

The official docs underdefine what escapes, if any, are supported but I don't think it'd be wrong to just crib the builtin python syntax region and get rid of the singe-quote ''' variant:

syn region  pythonString
      \ start=+[uU]\=\z('''\|"""\)+ end="\z1" keepend
\ contains=pythonEscape,pythonSpaceError,pythonDoctest,@Spell

[amcsi]

TIL