Sort symbols by address, then parentage, then index

[Rangi42]

Fixes #1151

With this file:

SECTION "test3", ROM0
Eggs:
 ret
 .end
Egg:
 ret
 .end
SECTION "test2", ROM0[3]
Quux:
 ret
 .end
Frob:
 .frob:
SECTION "test", ROM0[0]
Foo:
 ret
 .end
Bar:
 ret
 .end
Baz:
 ret
 .end

The previous .sym output was this:

00:0000 Foo
00:0001 Foo.end
00:0001 Bar
00:0002 Baz
00:0002 Bar.end
00:0003 Baz.end
00:0003 Quux
00:0004 Frob
00:0004 Frob.frob
00:0004 Quux.end
00:0004 Eggs
00:0005 Egg
00:0005 Eggs.end
00:0006 Egg.end

And the fixed .sym output is this:

00:0000 Foo
00:0001 Foo.end
00:0001 Bar
00:0002 Bar.end
00:0002 Baz
00:0003 Baz.end
00:0003 Quux
00:0004 Frob
00:0004 Frob.frob
00:0004 Quux.end
00:0004 Eggs
00:0005 Eggs.end
00:0005 Egg
00:0006 Egg.end

(Any particular sorting is not guaranteed by the man page, and .sym output is not something we've previously tested, so this isn't one of the CI test cases; just something to demonstrate the change for review.)