replacing lena in examples and most tests
adding name to contributors
renamed gabors
removed lena reference
modified array
Modified docstring
removed typo that caused test error
Use equal_nulp for more robust test comparison
Update edge detectors to produce values in [0, 1] and clean up tests
Document threshold scaling
Remove prints in test suite
Merge pull request #1221 from stefanv/pr_1126_update

ENH: Replace lena with astronaut