RegularExpressions chapter exists in both UPBE and DeepIntoPharo

[dmitrizagidulin]

(Extracted from #133)

We should consider de-duplicating the RegEx chapter -- it exists both in this book and in DeepIntoPharo.

[kilon]

Just for shake of disussion Deep Into Pharo is reference based PBE is tutorial based. We can briefly mention regex with some practical examples where we mention string manipulation and reference Deep Into Pharo book.

[Ducasse]

Yes this is the idea.
So the regex chapter can be removed or just a simple example.
In fact a chapter Bolts and nuts with a bit of file and regexp would do it.