Leave from single INI file

[odashi]

Current NMTKit uses INI files for all configurations (see the sample script) and this lacks some flexibilities for model re-writing. We always need to modify large INI file even if changing only 1 configuration.

Our interest is below:

• Separating global configurations and experiment-specific configurations.
  1. Allowing to specify multiple script files in --config option.
  2. Placeholder option, e.g. if the option is set to NULL, then users should give actual parameters through the command line.
• Allowing to use other data format (JSON, XML, etc.) that could store more structured options in exchange of redundant writings.