Refactor of error handling and badger db in-memory mode

What's Changed

• [tablesize]change the default to 2GB by @jingweicb in https://github.com/coinbase/rosetta-sdk-go/pull/438
• [types]remove two fields in preprocess request by @jingweicb in https://github.com/coinbase/rosetta-sdk-go/pull/439
• replace a comment by @jingweicb in https://github.com/coinbase/rosetta-sdk-go/pull/445
• Error handling refactor by @GeekArthur in https://github.com/coinbase/rosetta-sdk-go/pull/446

Full Changelog: https://github.com/coinbase/rosetta-sdk-go/compare/v0.8.0...v0.8.1