Make it possible to listen to a certain interface

...not just port.

This commit also updates the INI example file on how to set this.
Not using `ini.File.Sections()`

I proposed this as a pull request[1]. It was not accepted. Doing things
the right way.

[1] https://github.com/vaughan0/go-ini/pull/1
Ignoring build executable
Removing pointer reference

Maps are called "reference types" for a reason.
Rename: `TriggerTrigger` => `Trigger`
Processing HTTP requests through a channel

This opens up to easily do rate limiting for each trigger.
Support rate limitting

This fixes #1.
Refactoring: externalize HTTP trigger trigger code
Make HTTP trigger optional

This is in preparison for supporting shell command triggers.
Support executing shell commands
Sorting imports

Keeping things nice and tidy.
Applying `gofmt`

To keep things nice and tidy.
Introducing Travis CI integration
Travis: Build status in README
Merge branch 'travis-ci'

* travis-ci:
  Travis: Build status in README
  Introducing Travis CI integration