Say "boot image" where that is what is meant

"Binary" was doing three jobs. It meant an SPBT file that the machine starts
from; it meant whatever the assembler happened to produce, which is now
either that or a loadable program; and it meant a compiled host tool. A word
that means three things means none of them, and the first of the three has a
name already - this project has been calling them boot images for a while
and the manuals had not caught up.

  Where it means an SPBT file       -> boot image
  Where it means either output      -> output
  Where it means a host executable  -> left alone
  Where it means base two           -> left alone

The user facing messages move with it:

  Error: No boot image specified.
  Usage: ./SplitBit [OPTIONS] <boot image>
  Error: This is not a SplitBit boot image.
  Error: This boot image is in format version 2, and this emulator reads 1.
  Successfully wrote SplitBit boot image to "hello.bin".

The assembler's own help was the interesting case. Its -o writes either
format, so "the binary" there was never right - it is "the output" now, and
the message that names the format is the one that says which it wrote.

No recorded output contained the word, so nothing needed re-blessing.
Checked before starting rather than after.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Source/Emulator/cpu.c

@@ -10,7 +10,7 @@
 uint16_t shiftRegister;
 
 // Reads one entry out of a vector table. Most significant byte first, matching the
-// branch instructions and the binary format.
+// branch instructions and both file formats.
 static uint16_t readVector(const uint8_t *programMemory, uint16_t base, uint8_t index) {
     uint16_t address = base + (uint16_t)index * VECTOR_ENTRY_BYTES;
     return ((uint16_t)programMemory[address] << 8) | (uint16_t)programMemory[address + 1];