Conrig V0.3.0

• Move ConfigPathMetadata::sys_config_dir, ConfigPathMetadata::sys_preference_dir
  and ConfigPathMetadata::sys_dir's implementation to ProjectPath.

Conrig V0.2.0

• Rename old ConfigFile to RawConfigFile, and add a checked version of ConfigFile.
• Add several unsafe methods to RawConfigFile to clearify the intention of some code.
• Remove collapse-io-error feature.

Conrig V0.1.0

• Add extra_files and extra_folders field to ConfigPathMetadata:
  Allow users to include external folders and files for searching and writing.

Conrig V0.0.0

This is an initial release and is not supposed to be used.