Add string expansion reporting

And fix line counting with expansion-made newlines.
This has the same bug as the old lexer (equs-newline's output does not
print the second warning as being part of the expansion).
Additionally, we regress equs-recursion, as we are no longer able to
catch this specific EQUS recursion. Simply enough, the new expansion
begins **after** the old one ends! I have found no way to handle that.

test/asm/equs-newline.asm

@@ -0,0 +1,4 @@
+
+ACT equs "WARN \"First\"\nWARN \"Second\""
+	ACT
+	WARN "Third"

test/asm/equs-newline.err

@@ -0,0 +1,8 @@
+warning: test/asm/equs-newline.asm(2): [-Wuser]
+    First
+while expanding symbol "ACT"
+warning: test/asm/equs-newline.asm(3): [-Wuser]
+    Second
+while expanding symbol "ACT"
+warning: test/asm/equs-newline.asm(4): [-Wuser]
+    Third

test/asm/equs-purge.asm

@@ -0,0 +1,2 @@
+BYE equs "PURGE BYE\nWARN \"Crash?\"\n    \n"
+BYE

test/asm/equs-purge.err

@@ -0,0 +1,3 @@
+warning: test/asm/equs-purge.asm(0): [-Wuser]
+    Crash?
+while expanding symbol "BYE"