Add SplitLint, and let it be told when something is deliberate

SplitLint reports valid assembly that has a shorter direct expression:
zero loads that could be RSTA or RSTB, Q moved through the stack where MVQA
would do, self-cancelling push and pop pairs, assignments overwritten
before use, unreachable fallthrough, one-byte pointer moves that could be
INCD or DECD, a branch to the label directly below it, a SETD reloading an
address the pointer already holds, and branches whose carry is known.

Its model is deliberately local and conservative: every label and every
directive forgets all known state, so a claim only ever lives inside a
straight-line region. It knows the calling convention - CALL forgets DP3
and keeps the rest, RCAL and SWI forget everything - and it shares
assembly.o with the assembler, so an added opcode cannot leave it holding a
private copy of the instruction table.

260 warnings across the corpus, of which three were wrong in the way that
matters: branchTest.asm and interruptFlagTest.asm exist to check that a
branch whose carry is known behaves correctly, so a diagnostic saying the
outcome is known is exactly right and exactly unwanted.

A line whose comment says "splitlint: <reason>" is now not reported on. THE
REASON IS REQUIRED and a bare marker is refused, because a suppression
nobody explained outlives whatever made it necessary. Suppressed warnings
are not counted, so --fatal-warnings does not fail on one, and the number
of them is printed at the end so the claim is visible rather than silent.

Tests/lint.sh checked a TOTAL: twenty three warnings expected, twenty three
found. That number stays right while the thing behind it goes wrong - a
rule that stopped firing while another fired twice would pass, and so would
a rule reporting at the wrong line. It now checks which warning came out
and at which line, that nothing else came out, and that the four lines
meant to stay quiet did. Confirmed by breaking one rule's message and
watching it name that rule: the old assertion passed the same sabotage,
because the warning still fired and the count never moved.

Written with the user while I was away; my part is the suppression
mechanism, the harness rewrite, and the three marks in the test programs.

Programs/testPrograms/branchTest.asm

@@ -46,7 +46,7 @@ bTaken:
   OUTA 0x00
 
   CCF
-  BNC cTaken
+  BNC cTaken            ; splitlint: this test exists to check a branch whose carry is known
   BRI wrong
 cTaken:
   CALL blankSpace
@@ -78,7 +78,7 @@ cTaken:
   INIB 0x01
   CCF
   ADD
-  BNC wrong
+  BNC wrong             ; splitlint: the point is that a set carry does NOT take this
   CALL blankSpace
   INIA 0d99             ; 'c'
   OUTA 0x00