rename logLikePoint->pointLogLike. It think this works better with
"point likelihood"
generateObs -> genObsPoint, to be consistent with pointLogLike
renamed marjLogLikeDeter -> trajLogLike. I don't think it makes sense to
call the product of all point log-likelihoods a marginal
log-likelihood. We're not really marginalising anything.
plotModelTraj -> plotTraj, so we can use it to plot data, too
simulateTraj -> simulate leftover
plotTraj documentation
rename infectious.period -> D to reduce typing load
make pointLogLike and genObsPoint operate on an "obs" column for consistency
logLikePoint -> pointLogLike leftover