Add a new text classification example, Interface & YAML util updates

Examples

• Fix typos (PRs #500, #501)
• Rename text_classification.py (PR #508)
• Move GLUE-specific code to general_language_understanding.py (PR #509)
• Upgrade the text classification script, supporting multiple evaluation metrics with GoEmotions example (PR #510)

Interfaces

• Add a new forward proc (PR #502)
• Fix potential bugs (PR #507)

YAML util

• Support call_method (PR #506)

Documentation

• Update projects (PR #498)

Misc

• Add repo_or_dir (PR #493)
• Update README (PRs #494, #496, #497, #499)
• Simplify example (PR #495)
• Update versions (PRs #492, #511)