Update README

with proposed API changes discussed with @JeffSpies
Merge branch 'dev' into feat/config
Move modules out of core into their own packages
Remove old handler and unused export-requirements files
Remove unused compat file
Update CONTRIBITING

includes class-based renderer example
[resolves CenterForOpenScience/modular-file-renderer#56]
Update setup.py
By default, mfr.detect returns a list of valid handler classes

Unless many=False, in which case only the first valid handler is returned
Registry is not a list instead of a dictionary

Namespaces for static assets are determined by a FileHandler class's
module name.

For example, if a FileHandler is located in mypackage.mymodule.MyHandler
and the STATIC_FOLDER variable is configured to be '/static',
the static assets will be copied to /static/mymodule/
Fix previewer
Switch ordering of Config init params
Add mfr_code_pygments configuration

pygments_theme and cssclass are configurable
Add all pygments themes
Show example of module-level config in previewer
Update README
Add readme and configuration files to template module
Show that config object is a dictionary
Rename previewer -> player
Update contributing docs
Add file handler methods for retrieving static asset URLs