Since #27 vmware-go-kcl has support the any logger interface,
which is very nice.
However due to the fact that `logger/zap.go` directly imports zap.
zap became a dependency of whoever uses `vmware-go-kcl.` The
problem is that zap also has many dependencies.
In order to avoid KCL users to pay a cost for a feature they don't
need, the zap stuff has been moved to a `logger/zap` sub-package.
Fixes#45
Signed-off-by: Aurélien Rainone <aurelien.rainone@gmail.com>
