Update dissolution_coefs docs to show nodematch(X, diff = TRUE) example

[smjenness]

For example:

nw <- network.initialize(1000, directed = FALSE)
age.grp <- sample(1:5, 1000, TRUE)
nw %v% "age.grp" <- age.grp

# durations = non-matched, age.grp1 & age.grp1, age.grp2 & age.grp2, ...
durs <- c(60, 30, 80, 100, 125, 160)
fit <- netest(nw, ~edges + nodematch("age.grp", diff = TRUE), 
              target.stats = c(450, 100, 125, 40, 80, 100),
              coef.diss = dissolution_coefs(~offset(edges) + offset(nodematch("age.grp", diff = TRUE)), duration = durs)) 
dx <- netdx(fit, nsims = 8, ncores = 8, nsteps = 300)
print(dx)

dx <- netdx(fit, nsims = 1, nsteps = 5000, keep.tedgelist = TRUE)
names(dx)

te <- dx$tedgelist[[1]]

te <- te[which(te$onset.censored == FALSE & te$terminus.censored == FALSE), ]
te <- te[, c("head", "tail", "duration")]

head(te, 25)
te$ag.head <- age.grp[te$head]
te$ag.tail <- age.grp[te$tail]

summary(te$duration[te$ag.head != te$ag.tail])
summary(te$duration[te$ag.head == 1 & te$ag.tail == 1])
summary(te$duration[te$ag.head == 2 & te$ag.tail == 2])
summary(te$duration[te$ag.head == 3 & te$ag.tail == 3])
summary(te$duration[te$ag.head == 4 & te$ag.tail == 4])
summary(te$duration[te$ag.head == 5 & te$ag.tail == 5])

[smjenness]

Will depend on Fixing #258 first, then update dissolution_coefs docs as above with working netdx example.