further modularizing code to parse configuration data

[mycoboco]

The current structure of cel/conf to parse a configuration file is not well modularized, that is, it is possible to further modularize the code that recognizes variables and thier values so that adding a new feature gets trivial by letting functions to perform sub-tasks be reused.

For example, when implementing a library to retrieve the configuration data from a configuration server built by using, say, ZooKeeper, stripping comments and expanding escape sequences in data from the server is not easy because those tasks are tightly bound with reading lines from a file.