Docs: reorg of the compiler.constants docs a little

basis/compiler/constants/constants-docs.factor

@@ -13,40 +13,55 @@ HELP: string-offset
 { $values { "n" integer } }
 { $description "hm" } ;
 
+HELP: vm-context-offset
+{ $values { "n" integer } }
+{ $description "Offset in bytes from the start of the vm struct to the context (ctx) field." } ;
 
 ARTICLE: "compiler.constants" "VM memory layout constants"
-"Common constants."
+"Common constants. All the values are given in relation to the bootstrap image being built."
 $nl
 "Constants that must match vm/memory.hpp:"
 { $subsections card-bits card-mark deck-bits }
 "Constants that must match vm/layouts.hpp:"
 { $subsections
-  alien-offset
-  array-start-offset
-  byte-array-offset
-  callstack-length-offset
-  callstack-top-offset
+  profile-count-offset
+  slot-offset
+}
+"Offsets to fields in the context struct:"
+{ $subsections
   context-callstack-bottom-offset
   context-callstack-save-offset
   context-callstack-seg-offset
   context-datastack-offset
   context-callstack-top-offset
   context-retainstack-offset
-  float-offset
-  profile-count-offset
-  quot-entry-point-offset
+}
+"Offsets to field in the segment struct:"
+{ $subsections
   segment-end-offset
   segment-size-offset
   segment-start-offset
-  slot-offset
-  string-aux-offset
-  string-offset
-  tuple-class-offset
-  underlying-alien-offset
+}
+"Offsets to fields in the vm struct:"
+{ $subsections
   vm-context-offset
   vm-fault-flag-offset
   vm-signal-handler-addr-offset
   vm-spare-context-offset
+}
+"Offsets to fields in data objects:"
+{ $subsections
+  alien-offset
+  array-start-offset
+  byte-array-offset
+  callstack-length-offset
+  callstack-top-offset
+  float-offset
+  quot-entry-point-offset
+  string-aux-offset
+  string-offset
+  tuple-class-offset
+  underlying-alien-offset
   word-entry-point-offset
 } ;