Changed default skill rust setting from "vanilla" to "int"

A new player creating their first character sees "skill rust: XX%"
listed when selecting their int value, but in "vanilla" rust it
actually has no effect.

It's more intuitive for things, out of the box, to work the way the
character creation implies they do.
Slight rearangement of reading logic, and styling.
Move book reading completion inside player class.
Make some player methods private.
Conceal book details until the player has studied the book a bit.
Add a const method for retrieving inventory contents.
Const some stuff.
Add method that checks whether the player either knows the given recipe or has a nearby book providing it.
Allow player to craft recipe if they have a book providing it nearby.
Only allow books to be used for recipe reference if you've read through them first.
Oxford comma can go to hell.
Replace kind of sloppy knows_or_has_recipe() with has_recipe() that returns the learn difficulty, and just call both when needed.
Add chance to memorize recipe when crafting out of a book.
Random whitespace cleanup.
Attempt to make chance of learning recipe from practicing it scale better.
Better phrasing for low-morale message.
Turn books_read into the generic items_identified.
Ease up on information blockade.
Only color-code books if the player has perused them.
Halve the rate of learning recipes from books.