Re-run image test + slanted labels export test
+ Contour plot image export
let username and api_key be a subset of creds

Now, saving username and api_key won’t overwrite other fields that may
exist in ~/.plotly/.credentials. Also, you can save more key-value pair
credentials to ~/.plotly/.credentials with:

```
saveplotlycredentials(‘example_username’, ‘example_api_key’,
struct(‘extra_key’, ‘extra_value’))
```
let the url endpoint be a config variable
Merge pull request #6 from plotly/variable_server_endpoint

Variable server endpoint
first tests of jpg, pdf, svg image exports
Update version; update image service url
more images
Merge pull request #9 from plotly/more_image_file_types

More image file types
Merge commit '70ddf36bda594de26315609c19cb19c702dd8c4a'

Conflicts:
	plotly/plotly.m
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_10.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_11.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_12.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_14.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_15.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_17.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_20.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_28.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_29.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_31.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_33.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_35.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_40.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_41.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_42.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_43.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_5.png
	plotly/tests/test_saveplotlyfig_images/PlotlyImageTest_9.png