More fixin'

[cormac-obrien]

This is a mish-mash of bug fixes and quality-of-life improvements, including:

• Console errors now flush the line buffer so you can actually see why something doesn't work. This was broken in the last PR (whoops).
• The viewmodel angle is finally correct! In order to correctly position the viewmodel, it has to be rotated in the reverse order as everything else, or it gets all wonky when the player is facing in the -X direction.
• I noticed by chance that the game panicked if the cursor couldn't be grabbed, which happened while I was tabbed into another workspace. Now it just emits a debug message.
• The engine now sleeps for 1 millisecond instead of yielding when running above host_maxfps. This reduces CPU usage by 2/3, from 3% of one core to 1%, on my machine.
• The --base-dir option is equivalent to the -basedir flag in the original game. It indicates to the engine the parent of the id1/ directory. If the id1/ directory is not found, Richter now helpfully logs an error explaining the problem and how to solve it. This is an improvement over the previous behavior, shared by the original game, which simply presents the cryptic message "gfx/palette.lmp not found".
• The find command has been implemented, which allows searching for cvars and commands from the console.

[cormac-obrien]

bors r+

[bors[bot]]

Canceled.