set date for what's new for this release

Updated whatsnew v0.7.2 (pvlib#953)

update whats new for pvlib#844 and other contributors (pvlib#851)

* update whats new for pvlib#844 and other contributors

* rebase

* epw docstring noqa fix

* update whatsnew date

* add anton. minor api.rst clean up

* escape asterisk

* add docs auto_examples to gitignore

* pep8

update whatsnew.rst, add contributors, v0.7.0 release date, address p…

…vlib#809 (pvlib#839)

* update whatsnew.rst, add contributors, v0.7.0 release date, address pvlib#809

* fix dotted line to match date line's length

add missing requests dependency (pvlib#726)

add missing requests dependency (pvlib#726)

remove appveyor and landscape

finalize 0.6.2 whatsnew (pvlib#724)

* finalize 0.6.2 whatsnew

* change 0.6.1 date format for consistency

* fix ghuser links

Update v0.6.1.rst

Add irradiance.clearsky_index (pvlib#571)

* basic code for irradiance.clearsky_index, still needs full docstring and tests

* Add a float conversion to irradiance.clearsky_index to allow integer inputs

* added tests for irradiance.clearsky_index

* fix typo in irradiance.clearsky_index test

* fix typo in irradiance.clearsky_index test

* Update pvlib/test/test_irradiance.py to remove extra spaces

* fixed incorrect documentation for irradiance.clearsky_index

* rename poorly-named variables in irradiance.clearsky_index

* truncate nan/inf values to zero in irradiance.clearsky_index

* update whatsnew and api.rst

* improved formatting to satisfy stickler

* preserve input nans for irradiance.clearsky_index

* remove trailing whitespace

* refactor irradiance.clearsky_index to simplify type-handling logic.  also changed behavior for input inf values to set clearsky index to zero

* revert change to inf/nan handling; input infs yield clearsky_index=nan