lightkurve/lightkurve: Lightkurve v2.0.0

Lightkurve v2.0.0 includes the following major changes: Removed support for Python 2. [#733] LightCurve is now a sub-class of astropy.time.TimeSeries. This enables the use of custom data columns and enables a closer integration with AstroPy. As a result, light curve objects now behave just like tables. [#744] The data search features have been modified to support and display community-contributed data products by default, and to support the new TESS exposure time modes (e.g. 20-second cadence). The CBVCorrector class has been re-implemented to enable users to remove instrumental noise from light curves in a way that is nearly identical to the method used by the official Kepler/TESS pipeline. The online documentation has been updated to include a dozen new tutorials, a new layout, and an extended API reference guide. [#926] The structure of the source code repository has been modified to separate source files (src/) from test files (tests/). [#947] See CHANGES.rst for an overview of several dozen smaller changes included this release