Some refactoring, renaming, and debug assertions for clarity and safety

- Add more `assume()` checks in the lexer
- Replace double negative "`disable* = false`" with "`enable* = true`"
- Naming convention of "`std::deque<> *Stack`" when relying on
  `.push_front()` and `.pop_back()`

include/asm/lexer.hpp

@@ -87,16 +87,16 @@ struct LexerState {
 	int lastToken;
 	int nextToken;
 
-	std::deque<IfStackEntry> ifStack;
+	std::deque<IfStackEntry> ifStack; // Front is the innermost `IF` block
 
 	bool capturing;     // Whether the text being lexed should be captured
 	size_t captureSize; // Amount of text captured
 	std::shared_ptr<std::vector<char>> captureBuf; // Buffer to send the captured text to if set
 
-	bool disableExpansions;
-	size_t expansionScanDistance; // Max distance already scanned for expansions
-	bool expandStrings;
-	std::deque<Expansion> expansions; // Front is the innermost current expansion
+	bool enableExpansions;
+	bool enableStringExpansions;
+	size_t expansionScanDistance;         // Max distance already scanned for expansions
+	std::deque<Expansion> expansionStack; // Front is the innermost current expansion
 
 	std::variant<std::monostate, ViewedContent, BufferedContent> content;
 

include/itertools.hpp

@@ -36,7 +36,7 @@ ReversedIterable<IterableT> reversed(IterableT &&_iterable) {
 // A map from `std::string` keys to `ItemT` items, iterable in the order the items were inserted.
 template<typename ItemT>
 class InsertionOrderedMap {
-	std::deque<ItemT> list;
+	std::deque<ItemT> list;                      // `deque` does not invalidate item references
 	std::unordered_map<std::string, size_t> map; // Indexes into `list`
 
 public: