add reference docker implementation

[mathematicalmichael]

Only thing I think needs verification is glog... how can I test that it's linked correctly? I left that line commented out and didn't edit the cmake file to find it, perhaps because libgoogle-glog-dev was already found? Not sure.

• built on something recent-ish as a base image. should be a good starting point and slightly more secure than what I built originally (see #15)
• eigen imports needed to be added once I was building on a newer OS (past 14.04)
• adds some image-related utilities
• fixes typo in BUILDING.md
• adds some usage examples via makefile in docker/ directory
• I have tested about 10 algorithms, but included syntax for just one so as not to bloat the makefile.
• I refrained from linking a docker-hub image. But if you'd like, I can publish one so that people can skip the build step. Should help with reproducibility just a bit more. Ideally though that would be built / published from the repo as an action.

Any and all feedback welcome.

[davidstutz]

Looks great, thanks for contributing and adding documentation :)

[mathematicalmichael]

@davidstutz do you happen to know how I can test if glog is linked correctly?