Anvil fixes (#4976)

* Rewrite to use wiki target/sacrifice terminology.

* Fix negative damages.

* Prevent repairing if output matches target.

* Make target and sacrifice const.

* Pre-PR tidy-up

* Keep m_MaximumCost updated.

src/Enchantments.cpp

@@ -85,7 +85,7 @@ void cEnchantments::AddFromString(const AString & a_StringSpec)
 
 
 
-size_t cEnchantments::Count(void)
+size_t cEnchantments::Count(void) const
 {
 	return m_Enchantments.size();
 }