Add `coverage_map` crate to provide `CoverageMapBuilder` and `CoverageMap` data structures #47

Job	Run time
fmt	5s
clippy	1m 23s
build	1m 45s
tests (file-store)	1m 15s
tests (ingest)	1m 28s
tests (mobile-packet-verifier)	1m 20s
tests (reward-scheduler)	34s
tests (task-manager)	1m 2s
tests-postgres (boost-manager)	2m 29s
tests-postgres (iot-config)	2m 13s
tests-postgres (iot-packet-verifier)	3m 7s
tests-postgres (iot-verifier)	2m 19s
tests-postgres (mobile-verifier)	2m 23s
tests-postgres (mobile-config)	1m 51s
build-release	0s
	23m 14s

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