Split up the package?

This package has become quite large and is something of a heavyweight dependency for packages that just need a single type. An example of that is StatsBase, which only uses DataStructures for the arrays as heaps stuff. Indeed, just going through and trying to fix the deprecation warnings in this package for more recent Julia versions has proved quite cumbersome. It seems to me that for the sake of maintainability, the easily separable pieces of this package could be split off into separate packages, say like Heaps.jl, Deques.jl, etc. That way packages can just pull in the functionality they need. Thoughts?

Start by reviewing the package structure and identifying the separable components mentioned in the issue, including heaps and deques, then inspect StatsBase's dependency usage. Compare the maintenance impact and deprecation-warning burden of splitting the package; done requires an agreed decomposition and migration plan rather than a single-file change.