Update documentation

Modify :meth: as {func} in documentation.

docs/tutorial.md

@@ -393,7 +393,7 @@ What's going on here? Let's step through the code.
 
 4. If there are existing SLiM mutations on the tree sequence we need to
     make sure any newly added mutations have distinct SLiM IDs,
-    so we use :meth:`.next_slim_mutation_id` to figure out
+    so we use {func}`.next_slim_mutation_id` to figure out
     what the next available ID is, and pass it in.
 
 

docs/vignette_coalescent_diversity.md

@@ -328,7 +328,7 @@ s = np.array([sum([sum([md["selection_coeff"] for md in m.metadata["mutation_lis
                   for m in site.mutations]) for site in ts.sites()])
 ```
 
-To do this, we used the `time=t` argument to :meth:`tskit.TreeSequence.samples`
+To do this, we used the `time=t` argument to {func}`tskit.TreeSequence.samples`
 to find the nodes alive at each of the two times (0 and 100 generations ago);
 then computed an array ``p`` of allele frequencies, with one row per site,
 the first column giving the frequency among the initial generation,