* stable on python 2

* Stable on python 2 and 3 (fixed utf-8 and ascii encoding issues)
 * Still needs compatible yara submodule update once pull request accepted

* * Fixed all encoding issues

* Proper error handling

* Updating yara submodule to reference yara patched with include callback support

* Updating submodule's branch

* Updating yara submodule

* Updating yara submodule

* Updating yara submodule

* Updating yara submodule

* Submodule update

* * Fixing memory leaks
* Fixing errors handling

* making error messages order consistent between include_callback and default yara behaviour

* Removing exception printing when callback fails

* Minor re-styling.

* Destroy compiler if PyCallable_Check(include_callback) fails.

* References to Py_None should be increased.

* Use Py_DECREF instead of Py_XDECREF for references that can't be NULL.

* Minor re-styling.

* Fix reference leak.

After calling Py_INCREF(include_callback) some code paths were leading to a return without calling Py_DECREF. Calling Py_INCREF before yr_compiler_set_include_callback is not necessary, as this function doesn't yield control to Python, but it should be called before yr_compiler_add_XX.

* Remove unnecessary calls to Py_INCREF/Py_DECREF.

The references were already incremented in yara_compile.

* Implement test case for include callbacks

* Point yara submodule to official repository.