Rephrase PURGE documentation and raise the default level to 2

Fixes #1847

man/rgbasm.1

@@ -441,10 +441,10 @@ or
 .Fl Wno-purge
 disables this warning.
 .Fl Wpurge=1
-or just
-.Fl Wpurge
 warns when purging any exported symbol (regardless of type).
 .Fl Wpurge=2
+or just
+.Fl Wpurge
 also warns when purging any label (even if not exported).
 .It Fl Wshift
 Warn when shifting right a negative value.

man/rgbasm.5

@@ -1711,15 +1711,21 @@ Note also that only exported symbols will appear in symbol and map files produce
 .Ss Purging symbols
 .Ic PURGE
 allows you to completely remove a symbol from the symbol table, as if it had never been defined.
+.Bd -literal -offset indent
+DEF value EQU 42
+PURGE value
+DEF value EQUS "I'm a string now"
+ASSERT DEF(value)
+PURGE value
+ASSERT !DEF(value)
+.Ed
+.Pp
 Be
 .Em very
-careful when purging symbols, especially labels, because it could result in unpredictable errors if something depends on the missing symbol (for example, expressions the linker needs to calculate).
-.Bd -literal -offset indent
-DEF Kamikaze EQUS "I don't want to live anymore"
-AOLer: DB "Me too lol"
-PURGE Kamikaze, AOLer
-ASSERT !DEF(Kamikaze) && !DEF(AOLer)
-.Ed
+careful when purging symbols that have been referenced in section data, or that have been exported, because it could result in unpredictable errors if something depends on the missing symbol (for example, expressions the linker needs to calculate).
+Purging labels at all is
+.Em not
+recommended.
 .Pp
 String constants are not expanded within the symbol names.
 .Ss Predeclared symbols