attach the list of downloaders to Papermonk

This will be helpful for investigating which downloaders are available,
plus it's better to use a local variable than a global that is just
aimlessly floating around.
make require("papermonk").Papermonk work

This exposes the Papermonk object immediately on the module. This is
nice for playing with the constructor instead of only using whatever
instance the module gives back by default.
write a pile of tests

There will also be tests that confirm that papermonk works inside of a
browser. But not yet.

Run the tests with:
    node tests.js

version bump to: v0.0.2
remove plan() calls because end() is called anyway
README: change section headers in markdown
README: art/bling because why not?
README: bibliometric -> bibliographic