Improvements and some new features

[fabn]

I like the idea and I often do this in my apps, so I took this gem and made some changes to fit my needs, let me know if you're interested in merge them. Here is a recap of what I did

• Removed unused files/modules/views etc. There is no point in keeping them into the gem.
• Automatically mount the engine at heartbeat endpoint (status is too common as word). I like to simply add gem 'new_relic_ping' in my Gemfile and have everything working out of the box.
• I made the above behavior configurable, one can change the endpoint, append it, prepend it or disable automounting using configuration methods.
• Simplified routes, only /heartbeat and /heartbeat/health available (removed the ping suffix).
• Added a newrelic_ignore call in the HealthController, heartbeat checks should not be reported as newrelic transactions otherwise they improve your apdex with no reason to do that. Obviously this is conditional and executed only if newrelic_ignore is available in controller.
• Updated the dummy app to run tests on latest rails.
• Changed the default database check to use default active record implementation which perform better and save some resources on busiest MySQL servers. Obviously that method is defined for each AR adapter.

I should add some test for the newly added features, but I'm not familiar with minitest I always used rspec.

Let me know what do you think of this.