Rewritten linguakit help text

[gentakojima]

I have rewritten the help output for what I consider is a more readable presentation. Please feel free to accept it as-is or use as inspiration for future work.

• Indentation and grouping headers are used to reduce verbosity.
• Modules are presented in the same order in both "Available modules" section and "Options for specific modules" section, for beter readability.
• Also some light rewriting and changes in capitalization in descriptions, for sake of understandability and readability.