`findfirst` instead of `index`?

[mattsignorelli]

Why not use firstfirst here?

AcceleratorLattice.jl/src/core.jl

Lines 40 to 47 in a43d413

	function index(str::AbstractString, substr::AbstractString)
	ns = length(substr)
	for ix in range(1, length(str)-ns+1)
	if str[ix:ix+ns-1] == substr; return ix; end
	end
	return 0
	end

[DavidSagan]

That was coded back when I was first leaning Julia and is not even used. I will remove it.