Enrich and standardize documents.

[kannapoix]

README says

Documentation is generated using yardoc

but I sees RDoc like sysntax, like +tx+.
Also there many methods which has no document and no description and class info about a parameter.
Now you are revamping this repository, so I think this is good time to enrich and standardize documents.
YARD or RDoc?

Any thoughts?

[etscrivner]

Feel free to contribute if this is important to you :) Otherwise, we will get to this as we have time.