Misc fixes

What's Changed

• Bump aws-sdk-sqs to latest version
• Bump Oj to latest version
• Introduce basic unit tests
• Safely load JSON documents using Oj.safe_load
• Rescue the appropriate parser error for Oj

Load JSON objects in strict mode

• Load JSON objects in strict mode by @darnaut in #49

Split mode + secondary indices

• Implement "split mode" that allows to run optica's cache instance in a separate process. Running optica in split mode results in significant reduction in CPU utilization on the optica instances, as well as reduction in workload that optica adds to Zookeeper cluster.
• Implement secondary index support. Previously, every request to optica would scan its entire dataset. This change allows to provide a list of fields to use as secondary keys, which can significantly improve performance of specific queries.
• Change reload_instances function such that it does full reload of cache only at specific intervals.
• Drop newrelic support

Allow configuration of Rack's key_space_limit

Merge pull request #45 from airbnb/rack-key-space-limit

Allow configuration of Rack's key_space_limit

Support for Datadog's tracing client

Merge pull request #44 from airbnb/ddtrace

Support for Datadog's tracing client

get_process_mem version pin to avoid crash

Merge pull request #43 from airbnb/ramya/fix-gem-version

get_process_mem set version to avoid crash

Support for sending events to SQS

• Support for sending events to SQS
• Use DogStatsD for tag support

Lock oj gem version to avoid ruby2.0 requirement

• Lock oj gem version to avoid ruby2.0 requirement

Performance Improvements, GC & JSON

• Use Oj as the JSON adapter, improves performance of get / by ~3x
• Fix for unnecessary cloning of cache results
• Add newrelic tracing for zookeeper requests

Enable garbage collection instrumentation

Adds an option to enable garbage collection instrumentation.