Color books with unknown contents red

This code should (SHOULD! please review carefully, since I'm not a code maestro) color all books that the player doesn't know the contents of red -- either because the player cannot read at all, or because the player hasn't yet skimmed the book.

I am open to suggestions of other colors. Red seemed like a good choice for "unknown." Maybe pink would be good, so it seems less urgent.
Update item.cpp
Formatting & error-fixes for book colors

Coding /is/ a perishable skill, after all.
Book color fix again

Whoops missed a paren.
Fix crash on sleep

The "lying down" disease would add the "sleep" disease which would invalidate the (implicit) iterator use by the range-based iteration.
Handle calendar::season_length without active world.
tweak to bloated zombie.
further range
Revert "further range"

This reverts commit af1eb2a166271a375a2e50aebcf48c0edb36591b.
Merge branch 'we-dont-need-no-bugs' of https://github.com/BevapDin/Cataclysm-DDA into merge
Merge branch 'tweak-bloated' of https://github.com/Lain-/Cataclysm-DDA into merge
Make advanced inv item moving take time
Fixed a leftover code that was blocking skill-up.  No big.
Advanced 2
Merge branch 'advanced-inv' of https://github.com/i2amroy/Cataclysm-DDA into fix