Custom environment table order

[jacebrowning]

In Python 3.6+ or with OrderedDict, the config metadata can maintain its order to control the layout of the environment table. Would you consider an option to make sorted() optional in this line:

pytest-html/pytest_html/plugin.py

Line 468 in 35a6100

for key in [k for k in sorted(metadata.keys()) if metadata[k]]:

[davehunt]

Id be happy to review a pull request, though if we can determine when the user has specified a type that maintains order and avoid adding any configuration options that would be great!

[jacebrowning]

Cool.

It might be as simple as sys.version_info >= (3, 6) or isinstance(metadata, OrderedDict).

Or just the latter condition if we want to be more explicit. Do you have a preference?