clarify Between

[JeffreySarnoff]

as given:

"""
    Between(first, last)

Select the columns between `first` and `last` from a table.
"""
struct Between{T1 <: Union{Int, Symbol}, T2 <: Union{Int, Symbol}}
    first::T1
    last::T2
end

• "between" may be understood as "through", inclusive of first and last
• "between" may be understood as "within", exclusive of first and last

if you intend "through", add e.g. first and last (including both) from a table
if you intend "within", add e.g. first and last (excluding both) from a table

[bkamins]

Fixed in 5c927b6. Thank you!