Remove Readline from std-lib

[ftarulla]

As an exercise for writing shards (and C-bindings), with @bcardiff we extract the Readline module and create a shard at crystal-lang/crystal-readline.

The v0.1.0 has the same code as in the Crystal std-lib.

[bcardiff]

While extracting this I also notice that the CRYSTAL_PATH gives more precedence to the std-lib rather than the shards.

Maybe instead of:

CRYSTAL_PATH="/usr/local/Cellar/crystal/0.31.1/src:lib"

it should be

CRYSTAL_PATH="lib:/usr/local/Cellar/crystal/0.31.1/src"

So Crystal 0.31.1 users can today add crystal-readline as a dependency and use it, even if it also exists in the std-lib.

[straight-shoota]

/cc #5215

[bcardiff]

It's not that I want to shrink the std-lib, but in the case of readline:

• it is not in the prelude,
• there is no solid specs,
• is no longer used for the compiler, and
• the implementation has not evolved in a long time. I doubt it is widely used.

Removing it will allow contributions in a simpler way probably and it is not critical for the std-lib.

[Fryguy]

Not sure how much history was in there, but it's a shame we lost the git history. In the future, we could use the following tool (disclaimer, I helped write it) - https://github.com/juliancheal/code-extractor (I also have it as a shell script in a gist here: https://gist.github.com/Fryguy/3490682c7761edeedba1ee28de5ed117)

[bcardiff]

The history is very minimal in this case. Like ~10 commits. Usually, I try to keep the repo.
Thanks for that script! It might help in the future.