Use newer Sequel gem

- there was a lot of depreciation warnings about dropping support of
  schema plugin in the future version.
- updated code to work without schema plugin
- refreshed other dependencies
- bump up gemspec

changes

bump up gemspec + add CHANGELOG

bump up gemspec version

Make library use possible

Would need rework, but it's now at least enough to discovere node

foo = Corona.poll host: '1.2.3.4', community: 'foobar'
foo[:model]

bump up gemspec

Migrate to 'asetus' for configs

bump up gemspec version

bump up gemspec

bump up gemspec version