Custom inspection with the `inspect` property is deprecated and will
not work in Node.js 11 anymore. This fixes it by using the custom
inspect symbol where existent and falls back to the old style in case
it does not exist.
closes#553
Update test: application -> use() should throw if not a function
Fix lint
Use arrow function
Refactor test using arrow function
Remove non mandatory brackets
fix for merge
Fix: missing refactor after merge
Use arrow function for old generator
closes#517
add index test for Application
add app.toJSON test
add test for app.inspect()
add tests for app.use()
add tests for app.onerror()
add tests for app.respond()
add tests for app.context()
add tests for app.request()
add tests for app.response
refactor for non-existence of test/app...js
no need for *.js
use helpers/ dir for non-tests
