Add: Asset FDB and merged bucket type

See merge request !133

1. Fix: Failed to get asset fro Asset type FDB.

1. Fix: Required Error type not set in case of delete operation

1. Fix: Error while updating data which is not present

1. Fix: Asset not saved to mixed bucket due to extra index field "name".
2: Fix: Failed to get saved asset due to missing "rowID" in index.

1. FIx: Error not handled on index update

Remove: Testdata folder/ Add: Testing readme

See merge request !132

Fix: File is being used by another process error on atomic write.

See merge request !131

1. Update: Testing readme

1. Update: gitignore to ignore testingdata folder

1. Remove: Test data folder because of size
2. Add: Testing guide in Testing.md

1, Fix: File is being used by another process error on atomic write. Closed temporary file conditionally,

Add: Redis as a cache to support grid mode

See merge request !130

1. Add: Exit if connection to redis server failed

1. Add: marshal with type check version. This saves allocations and time if existing data is string or []byte.
2. Fix: Typos.
3. Add: Benchmarks for marshal and marshalWithTypeCheck

1. Add: Check redis connection on setup

1. Add: Save by adding provided prefix.
2. Add: Set() method will add default expiration time.

1. Add: Purge redis cache

1. Add: Redis cache to cache configuration

1. Refactor: Unit tests

Add: Unit tests

1. Fix: panic in redis cache object is nil

added encryption support in fdb

See merge request !128

1. Add: Redis as a cache support for grid mode. Redis implements cacher interface.

1. Add: Cacher interface and cache types. Fastcache implements this interface.