KeplerGO/lightkurve: Lightkurve v1.0b20

v1.0b20 includes the following changes: We adopted a rule that all method names must include a verb, and all class properties must be a noun (cf. #286). As a result, we renamed the following methods: LightCurve.cdpp() is now LightCurve.estimate_cdpp() LightCurve.periodogram() is now LightCurve.to_periodogram() LichtCurve.properties() is now LightCurve.show_properties() TargetPixelFile.aperture_photometry() is now TargetPixelFile.extract_aperture_photometry() TargetPixelFile.centroids() is now TargetPixelFile.estimate_centroids() TargetPixelFile.header() is now a property. Added Periodogram.smooth() (#288). Periodogram.estimate_snr() was renamed to Periodogram.p.flatten() (#290). Lightkurve can now read in light curve files produced using LightCurveFile.to_fits() (#297)