Add RouteView parser and enable ASN annotations

[stephen-soltesz]

This change adds a routeview package for parsing and searching the RV data. This will be used by the ASN annotator.

Search uses golang sort.Search. ParseRouteView is designed to reduce memory requirements as much as possible. This is accomplished in two ways:

• Smaller netblocks are merged with larger netblocks when Contains() is true and ASNs match. (saves ~40MB)
• Because many ASNs are duplicates, IPNet instances reference string pointers. (saves ~4MB).

This was the best of four approaches as benchmarked from sandbox-soltesz-scratch, including:

• annotation-service/asn.LoadASNDatasetFromReader
• ParseRouteView without netblock coalescing
• ParseRouteView with early Systems parsing

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 129

• 75 of 75 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.6%) to 81.33%

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Totals
Change from base Build 122:	3.6%
Covered Lines:	379
Relevant Lines:	466

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💛 - Coveralls

[stephen-soltesz]

https://github.com/m-lab/dev-tracker/issues/534