Updated readmes
Added MIN_USER_UID constant to config
Added BASE_RID constant to AD constants
Removed UID_FIELD as an LDAP requirement for CifUser
Implemented Active Directory SID-based UID generation for users, with unit test
Improved caching to reduce runtime
Removed unnecessary loop
Improved CifLdap tests
Removed CifUID because it is no longer needed, updated roadmap
Added basic introduction to LDAP
Added brief introduction to Kerberos