Improve redis serialization

Improve serialization when manually adding to redis cache

Enhance concurrency behavior

• Enhance when handling safe http method

Fix redis response

• Fix sending duplicate response slices when facing big payloads

Redis cache #get fix

Fix minor bug found while using manual caching with redis

Head request patch

Fix head request handler

Koa support

Add Koa 2 support

Redis cache patch

Fix _acquireLockWithId reference (thanks @it4mag)

Important patch

Add compressible missing dependency (thanks @rrgarciach)

Redis cache lock fix

Fix RedisCache#releaseLockWithId

New option and better default behavior

• add optimizeDuration option
• set 'private' cache when fit