style-guide: Define (and capitalize) "ASCIIbetically"

The style guide didn't give any definition for it.

src/doc/style-guide/src/items.md

@@ -478,8 +478,8 @@ foo::{
 A *group* of imports is a set of imports on the same or sequential lines. One or
 more blank lines or other items (e.g., a function) separate groups of imports.
 
-Within a group of imports, imports must be sorted ascii-betically. Groups of
-imports must not be merged or re-ordered.
+Within a group of imports, imports must be sorted ASCIIbetically (uppercase
+before lowercase). Groups of imports must not be merged or re-ordered.
 
 
 E.g., input:
@@ -507,7 +507,7 @@ re-ordering.
 
 #### Ordering list import
 
-Names in a list import must be sorted ascii-betically, but with `self` and
+Names in a list import must be sorted ASCIIbetically, but with `self` and
 `super` first, and groups and glob imports last. This applies recursively. For
 example, `a::*` comes before `b::a` but `a::b` comes before `a::*`. E.g.,
 `use foo::bar::{a, b::c, b::d, b::d::{x, y, z}, b::{self, r, s}};`.