improvement of osc_sanitizeString

osc_sanitizeString: added single quote to hyphen conversion

@TODO: use user-defined stop words when sanitizing slugs URLs
Merge branch 'patch-19' of github.com:emanwebdev/Osclass into e19

Conflicts:
	oc-includes/osclass/formatting.php
Merge pull request #1366 from osclass/e19

E19