DOC: various peculiarities of make bitset!

[dockimbel]

@meijeru commented on Tue Apr 18 2017

1. charset is shorthand for make bitset! except it does not cover make bitset! <binary>. This does make sense since charset suggests we deal with code point numbers, but it is useful to point out.
2. charset 5 makes a single-byte empty bitset, charset #"^E" makes #{04}, BUT both charset [5] and charset [#"^E"] make #{04}. In other words, make bitset! <integer> is treated as storage reservation, as with all series! values, although bitset! does not belong to series!. It is questionable which kind of (in)consistency is less confusing for the user. In any case, the chosen solution has to be documented...
3. charset [32 - #"Z"] is allowed, in other words, integers and code points may be freely mixed in the spec block.

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@meijeru commented on Wed Apr 19 2017

Point 3 is solved by the fixes to #2587