SLIME + Named readtables

[73budden .]

Hi!

I have made a readtable-related pull request long time ago, it was not
merged because it was breaking things that worked before.

So I suggest to discuss another approach to SLIME + NAMED-READTABLES
cooperation.

Please see the essay here:

https://bitbucket.org/budden/clcon/src/e3c40c555295336a3a13c506cce6a179f9dd8713/doc/how-to-support-readtable-with-slime.md?fileviewer=file-view-default