Adding serviceFn

[ragboyjr]

• Added new serviceFn function to create service functions
  instead of classes
• Refactored service into serviceFactory to share code between
  serviceFn and service.

Signed-off-by: RJ Garcia rj@bighead.net

[ragboyjr]

This could resolve #103

[young-steveo]

Thanks for the PR!

I think I can be convinced that an "injectable factory" method like serviceFn is a good addition, but I would make a couple of suggestions for this PR:

• The main difference between this new function and the bottle.factory is that this factory will be injected with dependencies as arguments to the factory instead of having the entire container injected. I think this should be explained in the Readme (as it stands it could be confused that bottle.serviceFn is exactly like bottle.factory)
• Don't expose serviceFactory internals to the public api. You can leave the bottle.service tests where they were, unchanged, and write some new tests for the serviceFn to show how it's different.
• I'm not keen on the abbreviated serviceFn name; none of the other bottle api methods use abbreviations, so it makes this one stand out. You could maybe rename it to serviceFactory, and then rename your internal serviceFactory to something else. This will align well with the current instanceFactory method name.

[ragboyjr]

Awesome, will do, all of your points sound good. thanks for taking the time to review!

[ragboyjr]

@young-steveo updated.