Create 4.2.2 release to fix missing files in 4.2.1

[tjkirch]

I'd like to request that a 4.2.2 release be created because the 4.2.1 gem was missing files -- see #391.

I've created PR #393 for the basic file changes. I'm not sure what else is involved, but I thought a tracking issue might help. Thanks!

[hsbt]

@drbrain @zzak Can you make hsbt at ruby-lang.org rdoc gem owner? I will release rdoc-4.2.2.

[drbrain]

@hsbt: done

[hsbt]

@drbrain Thank you!

@tjkirch Released rdoc-4.2.2