python-ldap talks in bytes,
as the rest of ldapcherry talks in unicode utf-8:
* everything passed to python-ldap must be converted to bytes
* everything coming from python-ldap must be converted to unicode

The previous statement was true for python-ldap < version 3.X.
With versions > 3.0.0 and python 3, it gets tricky,
some parts of python-ldap takes string, specially the filters/escaper.

so we have now:
*_byte_p2 (unicode -> bytes conversion for python 2)
*_byte_p3 (unicode -> bytes conversion for python 3)
*_byte_p23 (unicode -> bytes conversion for python AND 3)