NEW: get_histogram

using the enhanced histogram of astroML
EHN: test
EHN: right plotting for bins='blocks'

unequal bins width supported only for plotting
EHN: bins default options
Merge branch 'master' into get_histogram

Conflicts:
	hyperspy/signal.py
Add User Guide entry, Examples and minor corrections to the docstring.
Merge pull request #1 from francisco-dlp/get_histogram

Get histogram
Correct typo
Merge pull request #124 from pburdet/get_histogram

Get histogram