Coding style: add a section on list ordering.

I've been keeping a lot of things (such as `Cargo.toml` package lists and `mod` declarations) in alphabetical order. This adds that preference to the style guide, so other contributors are aware of it.

Cargo.toml

@@ -32,31 +32,31 @@ libtock_temperature = { path = "apis/temperature" }
 libtock_build_scripts = { path = "build_scripts"}
 
 [profile.dev]
-panic = "abort"
-lto = true
 debug = true
+lto = true
+panic = "abort"
 
 [profile.release]
-panic = "abort"
-lto = true
 debug = true
+lto = true
+panic = "abort"
 
 [workspace]
 exclude = ["tock"]
 members = [
     "apis/adc",
     "apis/air_quality",
     "apis/alarm",
-    "apis/gpio",
+    "apis/ambient_light",
     "apis/buttons",
     "apis/buzzer",
     "apis/console",
+    "apis/gpio",
     "apis/leds",
     "apis/low_level_debug",
     "apis/ninedof",
     "apis/proximity",
     "apis/temperature",
-    "apis/ambient_light",
     "panic_handlers/debug_panic",
     "panic_handlers/small_panic",
     "platform",

doc/Style.md

@@ -1,6 +1,21 @@
 Coding Style
 ============
 
+## List Ordering
+
+Source code tends to contain many lists whose order is unimportant, such as
+dependency lists in `Cargo.toml` and `mod` declarations in `.rs` files. When
+there isn't a better reason to prefer a particular order, these lists should be
+in alphabetical order.
+
+Benefits:
+
+1. When lists become long, this makes it easier to search for a particular
+   entry.
+2. Always adding new entries at the bottom of the list results in merge
+   conflicts whenever two PRs add entries to the same list. Putting them in
+   alphabetical order decreases the probability of merge conflicts.
+
 ## Naming Conventions
 
 Many things in `libtock-rs` live outside Rust's namespacing system, and can