Started working on #11 - adding sub-domain support

Most of the basic stuff is in place - the language is recognized from a
xx. sub-domain(en.|bg.|etc). Most of the URL's are being rewritten
correctly.
Needs some more testing though.
Started working on sub-domain support. Authentication functions will be overwritten when possible.
Added sub-domain support(#11).
Added a fairly stable support for sub-domains - still needs more testing though.
Logged-in cookie is being set for all sub-domains(the cookie is set with ".example.com" for the domain), so that the user can be recognized.
It's possible to allow the creation of the auth_cookie as well, if you hook to the "mlwp_set_sd_auth_cookie" filter and return true.
This is disabled by default for security reasons.
Additionally some issues with the rewrite rules generation have been fixed as well.
Revert "Added sub-domain support(#11)."

This reverts commit afb75586d547eb4047ae1acfa814bdfda3c39b04.
Revert "Revert "Added sub-domain support(#11).""

This reverts commit 8fa3c2c5fa6b8af5d81f80989cd18d571c75906c.
Added the "mlwp_set_sd_auth_cookie" filter.
Hook to that and return true in order to enable authentiaction cookies on all sub-domains(not suggested in general, due to the possible security issues).
Merge branch 'subdomain-support' into dev