Adds a local service for decorating IPs with annotations.

[pboothe]

Does not (yet) hook it up to main.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 160

• 124 of 126 (98.41%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 99.707%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
geoannotator/ipannotator.go	16	18	88.89%
<!--	Total:	124	126	98.41%	-->

Totals
Change from base Build 152:	-0.3%
Covered Lines:	681
Relevant Lines:	683

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💛 - Coveralls

[pboothe]

annotate is the service, ip is the annotation function being called. When I imaging extending this code to annotating new things, I think I would prefer to write a different handler with different input and output handling and types to handle annotating different input datatypes. So I wanted the input datatype to be part of the base URL to allow the http.Muxer to delegate to the right handler instead of having to put that logic in there myself in the future.