Makefile should use repos of optmatch and RItools

[josherrickson]

load.R loads optmatch and RItools via library. Should switch to devtools::load_all(), but may need to be smart about it e.g. devtools::load_all(../optmatch) works on my machine, but what happens if optmatch and optmatchExperimental don't share a parent directory? Maybe add a check if ../optmatch exists, and fallback to library as needed. This is a minor problem now, but noting in case someone in the future expects features that aren't pushed to CRAN yet.

[benthestatistician]

Poor man's alternative: specify minimum versions of optmatch and RItools in DESCRIPTION. Set up a warning message of some sort that points users to those packages' github repos in the event that optmatchExperimental fails to build for this reason.