Comprehensive namespace cleanup.
Clean up namespacing in accounts system too.
- drop `where` from all on_use/on_test (it is no longer being passed in)
- allow `api.use(package, {options})` without where
- fix showdown to use a weak dependency
Drop all @export lines. Add api.exportSymbol instead.
first stab at dropping the @export comment parser
update awssum
test-packages now has no immediate server-side errors (client-side, sure)

eliminate accounts-urls package
most tests pass, just not coffeescript
fix coffeescript.  test-packages passes!
Get rid of linkerFileTransform.