fix python 3.7 build on travis (pvlib#634)

* update try python 3.7

* 3.7dev

* new resize operation

* whats new, comment

initial implementation of pvsyst_celltemp function (pvlib#552) (pvlib…

…#628)

* initial implementation of pvsyst_celltemp function (pvlib#552)

* Reformat for stickler-ci

* Add error tests for pvsyst_celltemp

* Remove unused variables per stickler-ci

* Add pvsystem.pvsyst_celltemp function to docs

* correct api title

* formatting changes per wholmgren and cwhanse

* Additional formatting improvements

* Fix symbol in Reference

finalize whatsnew v0.6.0 (pvlib#575)

* finalize whatsnew v0.6.0

* add contributors

* add code formatting, links, add v prefix to 0.7 (pvlib#6)

* update date

* update date

add license, docs, authors to manifest, exclude spa files (pvlib#580)

add license, docs, authors to manifest, exclude spa files

codecov, deploy git tags to pypi with travis (pvlib#572)

* add codecov to .travis.yml

* add pypi deploy key to travis

* add .codecov.yml, add deploy

* remove bad yml

* add coveragerc

* change deploy env condition

* add codecov badge

update joss paper DOIs (pvlib#544)

* add joss badge [skip ci]

* add holmgren2017 doi

* add doi [skip ci]

* add mikofski2017

* update pvlib doi [skip ci]

finalize whatsnew

finalize 0.5.1 whatsnew (pvlib#385)

set 0.5.0 release date

add release date to whatsnew