Drop AnchorLayout, merge its features into FixedLayout.
#!/usr/bin/env python3
import sys
sys.path.append('..')
from tuikit.core.events import KeypressEvent
x = KeypressEvent('tab', '\t', set(['shift', 'ctrl']))
print(repr(x))
print(x.mod_key())
x = KeypressEvent(None, 'c', set(['shift', 'ctrl']))
print(x.mod_key())