Use unicode for LdapAttribute internal values

All internal values of an LdapAttribute should be converted to unicode.
- __unicode__ can return them as is
- __str__ returns them utf-8 encoded

Fix a TypeError error when passing an unicode dn to LdapNode constructor

Use utf-8 encoded credentials for LDAP binds
Merge pull request #17 from eonpatapon/unicode_fixes

Use unicode for LdapAttribute internal values
Add documentation about PATH settings on Gentoo
Merge pull request #19 from xhochy/hotfix/os-specific-doc

Add documentation about PATH settings on Gentoo
Expose dn as a read-only property of LdapNode
Merge pull request #22 from leonhandreke/feature/expose-dn

Expose dn as a read-only property of LdapNode
Decode strings as utf-8 when converting to unicode
Merge pull request #23 from leonhandreke/bugfix/decode-attribute-as-utf8

Decode strings as utf-8 when converting to unicode
add unittests for ldapom
tests for get_ldap_node and retrieve_ldap_node
change documentation format to doxygen
change documentation style to doxygen in openldap/__init__.py