region management / remove redundant computation

[yakra]

Closes yakra#220. Removes an unused vestigial variable.
Closes #523.
Closes #522.

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C++ Region management:

• A step toward making siteupdate "Valgrind clean". Rather than manually create new Region objects on the heap and store pointers in a vector, Regions are emplaced in a list. (I'd prefer a vector, but can't because Region contains a std::mutex, which is immovable, making Regions immovable too. Went with this instead.)
  I don't have to manually delete anything, as the list destructor cleans the objects up at the end of the program when the list goes out of scope.
  Next up: TravelerLists.
• In the process, changed the Region ctor to throw if the regions.csv line has the wrong # of fields. AIUI that's considered better practice than setting & checking a valid bit and deleting a fully constructed object, popping it from a container, etc. Cleaner code either way, and a tad less RAM.

[yakra]

Going to take a closer look at this one. May reopen in a few... hours? Days?

[yakra]

Expected to re-open this after double-checking all my silly benchmarks.
Around the time I closed it, I found a couple things to optimize in TravelerList::userlog. One (counterintuitively) didn't pan out, but the other did. A decent performance boost under FreeBSD -- not as much as I'd hoped, but an improvement nonetheless.

Meanwhile, I've hit upon a way to get Region objects into contiguous memory, mutexes and everything. All I've got to do is:

• Refactor the code that reads .wpt & .list files out into a new reusable function. (Done!)
• Write a new .csv parsing routine. (Mostly done, as a separate program not integrated into siteupdate yet.)
• Change the Region constructor to take fields as args instead of a whole line. (To do.)
• Write a custom container class. (To do.)

Easy, right? 🤣 This will pay off when I get around to arranging HighwaySystems, Routes & HighwaySegments contiguously.

[yakra]

A decent performance boost under FreeBSD -- not as much as I'd hoped, but an improvement nonetheless.

Found a way to take it a step farther. Be a few hours before I can test on bsdlab (just started BiggaTomato) but the concept looks promising.