Compatibility issue with recent NaMaster update #24
Description
Recent updates in NaMaster caused some compatibility issues for bbpower.
For example, function argument changes in nmt.NmtBin since NaMaster commit 2b35f37af22f8b9c8d7738fc71f57f68a3f98afb. This causes line 133 in powerspector.py to fail. @susannaaz @kevguitar @damonge