docs for Demography.add_population_split() (and others) parameters are unclear

[grahamgower]

Docs for the following Demography methods: add_population_split(), add_admixture(), add_mass_migration(), add_migration_rate_change(), add_simple_bottleneck(), add_instantaneous_bottleneck(); all have problematic formatting of types in the parameters section. In addition, they all accept either an integer ID, or alternately a population name, as source/dest/population/etc. param, but this is not clear from the docs.

[jeromekelleher]

Well spotted. Looks like there's a sphinx formatting issue, but also it would be good to link to the identifying populations section to clarify this point.