fix #25 and set up future Mac testing on Travis

~~Mostly opening this to see what the combined status indicators between AppVeyor and Travis look like, don't merge this.~~

This contains a fix for #25, simultaneous loading of incompatible libsundials_cvode and libsundials_cvodes. It also sets up the installation steps for future testing of both Mac and Linux on Travis, once Travis starts accepting more repositories for multi-OS support.