The "run" subcommand requires the path of a config file.
"*Config" stores the consumer key and secret pair.
Implement the serialization and deserialization of "*Config" by using "encoding/json".
The description of "fibot" command is written in "cmd/fibot/commands/app.go".
Fix: Pass a value typed as "io.Writer" to "json.NewDecoder".
Wrap "*configJson" with "*Config" to make "Key" and "Secret" unpublic.
Ignore "*.json" to avoid to track the config file with Git.
Load the configuration of fibot from a JSON-formatted file.
Merge branch 'feature/command-run'