Feature request: `FOR / REPT ... ELSE` like Python

Like it says on the tin.

```asm
REPT 1
print "Hello "
ELSE
println "world!"
ENDR

REPT 1
BREAK
ELSE
FAIL "Not reached!"
ENDR
```

The issue does not name implementation files or tests. Start by locating the existing FOR, REPT, ELSE, BREAK, and ENDR handling in the assembler, then inspect related parser tests. Done means the shown REPT examples assemble with the expected branch behavior, including BREAK skipping the ELSE body.

Written by the indexing model from the issue text.