Docstring added to ETdetector.overlap_exp()
Docstring written for ETdetector.orf_no_frequency()
ETdetector.overlap_reduction_function() for non-frequency

Computes orf from detector IDs (1, 2, 3), polar and azimuthal angles.

This doesn't work with frequency dependent orfs.

	modified:   modules/ETdetector.py
Change ETdetector.overlap_reduction_function() to run with no error
Plot values of functions of polar and azimuthal angle
Ignore directory called _build
Remove type-checking of input for ETwaves.principal_polarisation_axes_0Psi()

Input arguments AZIS and POLS can be any any number or numpy array of numbers.
If they're more than 1-D, then they will be flattened by numpy.outer().

All arguments will be first converted into numpy.array.  If they don't
already contain just numbers, there will be an error raised when the
outer product is taken.

Test in tests/ETwaves/principal_polarisation_axes_0Psi.py is modified
accordingly and passed.

	modified:   modules/ETwaves.py
	modified:   tests/ETwaves/principal_polarisation_axes_0Psi.py
Integrate a function of sky position over solid angle

Test written and passed for integrating a function of
polar and azimuthal angle over solid angles.

	modified:   modules/ETutils.py
	new file:   tests/ETusefuls/integrate_skyfunc.py
First ipython notebook