Please expose .Internals

Nobody has claimed this yet.

It would be great to have access to some unsafe or just convenient internals. To give two simple examples of each:

* I may want to use `insert'` instead of the Ord instance to provide Ord-free API to the user for a function I'm internally using pqueue in.
* I may have external knowledge about element I'm inserting. For example I may know that new element is maximal for a given MinQueue. Currently `insert` will perform `n` comparisons on the key. With .Internals I could write `unsafeSnoc` that does not do the comparisons along the way, saving time.

Many popular Haskell packages already expose this module. Some choose to not expose it in Haddock documentation (I'd recommend against that). It'd be great if `pqueue` could as well with the usual disclaimers about no guarantees to the contents.

Start by locating the pqueue source definitions for insert, insert', and MinQueue, then review how the package exposes modules and Haddock documentation. Done means an Internals module provides the requested convenience or unsafe operations with the stated lack-of-guarantees disclaimer and corresponding documentation.

Written by the indexing model from the issue text.