wip: refactor to promise-based approach

TODO:
 * check tests
 * update version notation in package.json
refactor: remove unused method
refactor: rename internal functions

Also remove unsused or commented function parameters.
style indent: use two spaced indention
refactor: add internal success/error handler
refactor binary-footer: change merge options order
refactor lib: reject w/ error when repo not exits
feat(cli-options): suppress email via --no-email option
refactor lib: merge options w/ default options
refactor test: update stubbing to work w/ promises
refactor test: we don't throw errors anymore
refactor test: reset stub and improve description
refactor test: update stubbing to work w/ promises
chore test: reduce timeout for test to 250ms
style: remove some blank lines
refactor markdown-reporter: make use of promises
test: add test for error callback
refactor test: remove obsolete test
refactor test: fix expectation
chore cli: lowercase help output