GSL not linked in final binary

[rhagenson]

A problem experienced by @HenningTimm and myself during an otherwise benign change (#39) is that the final binary is not properly linked against GSL.

I personally have tried the following:

• Manually purging an reinstalling libgsl-dev
• Setting up a conda environment and installing the gsl package that way

Neither of these fixed the GSL linking problem* and I suspect the issue is somewhere in either our use of rgsl or within rgsl itself. There are instructions on rgsl for linking to GSL v2, however we already follow those instructions via addition of the "GSL/v2" feature in Cargo.toml here.

* I am away from the machine where I experienced this GSL linking problem so will copy the error message into this thread later this evening.

[rhagenson]

Simulated a fresh install via running the rust:1.41.0 container from DockerHub, installing libgsl-dev and libgsl23, then cargo install rust-bio-tools and I have no problem with linking to GSL.