Make StrPack work with Julia 1.5

[lukemerrick]

I'm brand new to Julia, so please be patient with me.

I tried add StrPack and it didn't work in Julia 1.5, so I cloned the repo and followed the Pkg.jl docs to re-create it as a package in the style described therein. Seems to install for me now.

I don't know that this is the right way to go about it, but it would be really great if this package could be adapted and registered (here: https://juliahub.com/index.html ?) to be easily installable with using Pkg; Pkg.add("StrPack").