Generate snippets for class methods

This patch teaches the auxillary PHP program to accept an optional
second argument: the name of a class.  If given then the program can
treat the first argument, the function name, as a method name if it
fails to find any ‘plain’ function by that name.  This makes it
possible for calls such as:

    $ php Create-PHP-YASnippet.php "push" "SplQueue"

If we fail to find a method we exit with a new error.  This will help
us know on the Elisp side whether we failed, for example, to provide
the correct class name.
Put class names in the ‘#group’ directive of snippets for methods

YASnippet lets us organize snippets into sub-groups.  We already look
for an extension name to put functions into a group with that name.
If we are creating a snippet for a method then we can also use the
name of the class that defines that method.  This patch implements the
logic to create such sub-groups for methods.
Teach payas/create-template to accept method and class names

This patch makes it possible to use

    (payas/define-template "push SplQueue")

to define a snippet for the SplQueue::push() method.  However, we only
change the underlying logic in payas/create-template.  This patch does
not teach the package to ask for the class name at any point.
Teach payas/report-error about ERROR_UNKNOWN_METHOD
Teach yas/create-php-snippet to prompt the user for a PHP class name

By using the prefix command (e.g C-u) the function will prompt the
user for the name of a class.  This lets the user create a snippet for
a class method.  We have to ask the user for the name of the class
because the package does not try to read it from the buffer.
Document support of the prefix command with yas/create-php-snippet
Update to version 0.7.0 for the method snippet support
Merge branch 'support-class-methods'

* support-class-methods:
  Update to version 0.7.0 for the method snippet support
  Document support of the prefix command with yas/create-php-snippet
  Teach yas/create-php-snippet to prompt the user for a PHP class name
  Teach payas/report-error about ERROR_UNKNOWN_METHOD
  Teach payas/create-template to accept method and class names
  Put class names in the ‘#group’ directive of snippets for methods
  Generate snippets for class methods