[speculative] Remove BioSequence(::Integer)?

[jakobnissen]

Right now you can do

julia> LongDNASeq(10)
10nt DNA Sequence:
CA--------

This strikes me as weak typing. In fact, we have not constructed a sequence from 10. Imagine a situation where you mistakenly thing x is something sequence-like, such as a bioseq or a string, but really, it's an integer. Doing LongDNASeq(x) then works - and give the wrong result.

I propose instead we change it to LongDNASeq(undef, 10), similar to arrays.