Potential flaw in grammar

Hello all,

I've been looking over the grammar to test out a parser I've been
building. I think i may have discovered a small flaw in the grammar
definition for string literals.

The problem is in the definition of heredoc-string-literal and
nowdoc-string literal. The relevant definitions:

from https://github.com/php/php-langspec/blob/master/spec/19-grammar.md#string-literals:

 heredoc-string-literal::
    hd-start-identifier   new-line   hd-char-sequenceopt  new-line
hd-end-identifier  ;opt   new-line

  hd-start-identifier::
    name

  hd-end-identifier::
    name

  nowdoc-string-literal::
    hd-start-identifier  '  new-line  hd-char-sequenceopt   new-line
hd-end-identifier  ;opt   new-line


According to my experience with these and example of a heredoc string would be:

   <<<TEST
  some string content here....
  TEST;

The grammar however makes no mention of the opening "<<<" and based on
what i'm seeing would accept something like:

    TEST
   abcdef
   TEST;

Which is not accepted by my version of PHP (5.5.9).

A second issue i noticed is in the definition of nowdoc-string-literal

An example nowdoc string taken from php.net looks like this:

   $str = <<<'EOD'
   Example of string
   spanning multiple lines
   using nowdoc syntax.
   EOD;

The grammar definition seems to be missing the opening single quote
and since it relies on on hd-start-identifier it is also missing the
required "<<<".

I think the following simple modifications should suffice, just wanted
to make sure i wasn't crazy before opening a pull request.

Change:
    hd-start-identifier::
        name
To:
    hd-start-identifier::
        <<< name

Create nd-start-identifier as:
    nd-start-identifier::
        <<< ' name '

And change:
    nowdoc-string-literal::
        nd-start-identifier  new-line  hd-char-sequenceopt   new-line
hd-end-identifier  ;opt   new-line


Thanks!
- Ken