RDoc 5.0

[zzak]

• json dependency: Removed strict dependency for json, it break to install ruby trunk(2.4) #412
• Drop Ruby 1.8 support
• RDoc 4.3 #395

[zzak]

@hsbt What are your plans for the json dependency?

I think we're using it for JsonIndex stuff, which I'd like to keep in RDoc if possible.

[zzak]

Ahh, I just saw #412

[hsbt]

@zzak I added comment for that issue.