changed Value field to unexported and created a Value() method
on each dynOpts type that contains logic to create a rsparser
in case the value field a configuration starts with prefix "~"
otherwise it will return the specified value
Moved engine/cdr.go to utils/cdr.go.
Moved engine/cdrs.go and engine/cdrs_test.go to cdrs package.
Moved api functions from cdrs/cdrs.go to cdrs/apis.go. Same for the
tests.
Deleted CDRsV1 type and its methods.