Add some more guidelines

Signed-off-by: Cole Miller <[email protected]>

STYLE.md

@@ -23,7 +23,7 @@ are every eight spaces.
 
 ### Braces
 
-K&R brace style: opening braces on the same line for `if`, `for`, `while`, and
+Opening braces on the same line for `struct`, `enum`, `if`, `for`, `while`, and
 `do`, but on a separate line for function definitions.
 
 `if`, `for`, `while`, and `do` always use braces, even when the body is a
@@ -38,6 +38,8 @@ single statement.
 
 Use only `/* */` in committed code, not `//`.
 
+Align end-of-line comments after struct field and enum variant declarations.
+
 ### Predicates
 
 Use explicit comparisons to 0 and `NULL`: `if (int_variable == 0)` and `if
@@ -53,3 +55,7 @@ Prefer functions to function-like macros in new code.
 
 Use defensive parentheses in the definitions of function-like macros, so that
 extra parentheses are never required around the arguments at call sites.
+
+### Functions
+
+In function bodies, cast an argument to `void` if it is unused.