put read-file functionality into new lib/readSchemaFile.js module. split out...

put read-file functionality into new lib/readSchemaFile.js module. split out command line interface and argument parsing functionality into own cli.js module, and make this module the command line entry point. old lib/main.js functionality moved to either cli.js or readSchemaFile.js. lib/main now is the main package module, which simply exports an object with sub-module functionality as keys (reader, writer, and schema).