kernel: Clean up svn-related code and data

* Rearrange sf18.13 version structure to
  + mention git hash and release offset,
  + separate OS release and kernel ABI numbers,
  + include an optional debug tag.
* Update the boot log and the blue screen to print the new fields.
* Update docs.
* No breaking changes.

Resolves #99.

kernel/trunk/macros.inc

@@ -5,16 +5,6 @@
 ;;                                                              ;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-__REV = 0
-
-macro $Revision a {
-  match =: Num =$,a \{
-    if __REV < Num
-      __REV = Num
-    end if
-  \}
-}
-
 ;// mike.dld, 2006-29-01 [
 
 ; macros definition