add efficient conversion from CString

[aplavin]

UnsafeArrays just provides a DenseArray wrapper around a pointer and length. Hope that adding this dep is fine!
In return, it gives almost zero-cost conversion from CString.

[aplavin]

bump!

[stevengj]

No, this is too unsafe. If the caller wants an unsafe array, they can use one themselves, but we can’t assume a CString pointer will remain valid after the call returns.

[aplavin]

That's unfortunate - users who need zero-cost conversion from C strings have to implement it manually every time

[stevengj]

If we wanted this, it would have to be a method of unsafe_wrap, not a constructor, since the semantics you are looking for mirror those of unsafe_wrap.