Avoid calling syntax-propertize-rules as may be unavailable.

Instead of using the macro syntax-propertize-rules, use the evaluated
macro. Older Emacs may not have the macro available, the final
function is short and easy to understand.

GitHub-Issue: 134
Guard propertize functions for Emacs that don't support it.
Merge commit '38e1940e950d47737fed30a5bd5d4e75e0faf103'

* commit '38e1940e950d47737fed30a5bd5d4e75e0faf103':
  Guard propertize functions for Emacs that don't support it.
  Avoid calling syntax-propertize-rules as may be unavailable.
Merge branch 'ejmr/highlight-variables-in-strings'

* ejmr/highlight-variables-in-strings:
  Add more tests for highlighting variable interpolation
  Create a unit test for highlighting interpolated variables
Update version to 1.13
README: Stress that I am looking for a new maintainer
Offer a prompt for documentation search
Added missing contributors

see release 1.2 changelog:
Urban Müller
Engelke Eschner
Add support for extended TAGS format

as produced by the tag tool in github.com/tekai/tools/
Prepend mode to auto-mode-alist to avoid other modes