Fix compiler warnings

Related to #15 (closed)

There's still a few more complex warnings to fix, but this is a good standalone change.

I've tested it here: /fred/oz016/tdavies/projects/testing/run_tdavies__fix_compiler_warnings/
It has the same injection results as /fred/oz016/tdavies/projects/testing/run_tdavies__tiebreak_clustering_on_template__inj_8000/run1/, which were run using a recent version of O4-dev

I also tried building it fresh using the bash script, since I'd had issues trying to make && make install on my dev repo. The most recent commit May have fixed it, or may be redundant but harmless.

Old

This branch is a little stale, and there's a couple more difficult warnings to fix, but each commit should correspond to a set of compiler warning fixes.