Room and lobby chat, /host, /fashion, player-colored lines, context tips, and American spelling

- Chat goes to your room (the sandbox, or your game) by default, and to the whole lobby with /all or a leading !.
  Lines from elsewhere say where they came from ([Sandbox], [Game 2]), lobby-wide ones from your room say [All].
  Typing shows only to your room. Protocol 8.
- Hosting: everyone is told who hosts now, and the host can hand it over with /host "player".
- /fashion <item> wears a fashion locally, like /color.
- Lines that mention a player show in that player's color, looked up as they draw.
- Tips are tagged with the item and situations they fit, and those that fit are 1.5x as likely. They turn over every
  10 seconds on one continuous run, show under the menu too, and can be turned off with Tips in HUD / Gameplay. The
  HUD hotbars hide while the menu is up (except on its item tabs).
- American spelling throughout: color, center, gray, mustache, and so on.

src/common.h

@@ -135,7 +135,7 @@ constexpr int RNG_SHIFT_B = 17;
 constexpr int RNG_SHIFT_C = 5;
 constexpr Uint32 RNG_SEED = 0x9E3779B9;
 
-// Describes a spray of square particles, fanned around angle by spread. Fill is how far their colour takes over their
+// Describes a spray of square particles, fanned around angle by spread. Fill is how far their color takes over their
 // black middle.
 struct Burst
 {
@@ -174,7 +174,7 @@ inline bool is_rect_overlapping(Rect a, Rect b)
     return a.x < b.x + b.w && b.x < a.x + a.w && a.y < b.y + b.h && b.y < a.y + a.h;
 }
 
-// Darkens a colour by amount, keeping its alpha.
+// Darkens a color by amount, keeping its alpha.
 inline Color color_shade(Color color, float amount)
 {
     return {color.r * amount, color.g * amount, color.b * amount, color.a};
@@ -185,7 +185,7 @@ inline Color color_fade(Color color, float alpha)
     return {color.r, color.g, color.b, color.a * alpha};
 }
 
-// A colour amount of the way from one to another.
+// A color amount of the way from one to another.
 inline Color color_mix(Color from, Color to, float amount)
 {
     return {from.r + (to.r - from.r) * amount, from.g + (to.g - from.g) * amount, from.b + (to.b - from.b) * amount,