feat: logging interface and default implementation

[sudeshrshetty]

Define generic logging interface for aries framework and provide default implementation.

[llorllale]

@sudeshrshetty what do you have in mind?

[sudeshrshetty]

//Logger - Standard logger interface
type Logger interface {

//Fatalf is critical fatal logging, should possibly followed by system shutdown
Fatalf(msg string, args ...interface{})

//Panicf is critical logging, should possibly followed by panic
Panicf(msg string, args ...interface{})

//Debugf is for logging verbose messages
Debugf(msg string, args ...interface{})

//Infof for logging general logging messages
Infof(msg string, args ...interface{})

//Warnf is for logging messages about possible issues
Warnf(msg string, args ...interface{})

//Errorf is for logging errors
Errorf(msg string, args ...interface{})

}

Custom implementation can be provided by calling logging.Initialize(customProvider) before using logger (means, before logging any lines).

Logging levels will be maintained by aries framework and it will be module based.
Like, each modules can have their own logging levels enabled.
Default logging level is INFO

[troyronda]

the discussion here looks useful:

• Proposal: Go 2: Create logger interface in the standard log package, with additional levels. Optionally add it to context package, too golang/go#28412
• proposal: log: change Logger to be an interface golang/go#13182