improve error correction and put behind ENABLE_MAGIC feature gate

[itdaniher]

This replaces Jaccard distance with Levenshtein distance error correction. The default match is delta-3, sufficient to match hp -> help, and all of: imagin, imogen, imagen, image, imagines, imahine -> 'imagine'

Require the / in groups to activate error correction.

Fix eval to work with expansion

[technillogue]

closing in favor of #94