BUGFIX: fix 1st order CRFB handling

For when the user tries to synth a 1st order CRFB modulator -
which happens to be the default form, so it seems worthwhile to
handle this gracefully.
FIX: xlim can be a 1d array.
BUGFIX: ensure no zero-length arrays are ever returned.
BUGFIX: raise syntax
Remove exec bit everywhere.
TEST: add test to test_axisLabels.py
BUGFIX: fix delaying 2d arrays.
Merge branch 'master' of https://github.com/ggventurini/python-deltasigma into tests

Conflicts:
	deltasigma/_delay.py
TEST: add more tests for delay()