Not able to add additional zapcores to flogo logger

[nareshkumarthota]

Current behavior:
No provision to add additional zapcore (like syslog zap core implementation) to flogo logger

Expected behavior:
Provision to add additional zapcores into flogo root logger.

What is the motivation / use case for changing the behavior?
Would like to add syslog support to the flogo logger.

Additional information you deem important (e.g. I need this tomorrow):
Couldn't able to inject syslog zap core into flogo logger with the flogo provided API, I ended up in refactoring flogo/core logger related files and same is available in my fork.

[nareshkumarthota]

Changes included:

1. Creation of new packages zapcores and zapconfig.
   zapcores: contains all registerd cores.
   zapconfig: contains default configuration and log level.
2. Refactoring existing zap.go such that before root logger creation all the available cores are appended together.

Example Usage:

1. User has to create zapcore implimentation. Sample syslog implimentation can be seen here.
2. User need to add the above created impl package to the first un used import.