Use string_types instead of basestring (PY3 compat).

A new fibe.py module has ben introduced to provide common tools
for PY3/PY3 comaptility.
Fix builtin  buffer usage (PY3 compat)
Use five.callable instead of builtin callable (PY3 compat)
Do not use dict.iter* (PY3 compat)
Fix imports of renamed modules (PY3 compat)
PY3 compatibility for __bool__ special method
More fixes for print_function (PY3 compat)