Optionally load did_you_mean (and RubyGems)
I just have opened PR 1, which allows Ruby to run when did_you_mean is not available. As I previously discussed in #16427, there are cases when speed, memory, disk or network bandwidth is a concern and did_you_mean is not useful for runtime. This is especially useful when Ruby is installed via packaging systems of (Linux) distributions.
The PR is split into 4 commits, because since I was there, I prepared similar changes to RubyGems.