Implement SIZEOF("Section") and STARTOF("Section") (#766)

Updates the object file revision to 8

Fixes #765

test/asm/section-sizeof-startof.asm

@@ -0,0 +1,8 @@
+SECTION "sect", ROMX[$4567], BANK[$23]
+	ds 42
+
+W = BANK("sect")
+X = SIZEOF("sect")
+Y = STARTOF("sect")
+
+	println "{W} {X} {Y}"

test/asm/section-sizeof-startof.err

@@ -0,0 +1,5 @@
+ERROR: section-sizeof-startof.asm(5):
+    Expected constant expression: Section "sect"'s size is not known
+ERROR: section-sizeof-startof.asm(6):
+    Expected constant expression: Section "sect"'s start is not known
+error: Assembly aborted (2 errors)!

test/asm/section-sizeof-startof.out

@@ -0,0 +1 @@
+$23 $0 $0

test/link/sizeof-startof.asm

@@ -0,0 +1,7 @@
+SECTION "meta", ROM0[0]
+	db BANK("sect")
+	dw STARTOF("sect")
+	dw SIZEOF("sect")
+
+SECTION "sect", ROMX[$4567], BANK[$23]
+	ds 42