feat: Std::String, Std::Map, Result/Option, ? operator, sizeof fix, docs

Add standard library modules:
- Std::String: strlen, strcmp, concat, copy, starts_with wrappers
- Std::Map: linear-probing hash map with String keys, int values

Add error handling:
- Result and Option algebraic enum examples
- ? try operator for automatic error propagation in HIR lowering

Compiler bugfixes:
- Fix sizeof() for user-defined structs (new hSizeOf HIR node)
- Fix HIR type lowering for char8, bool8, int8, uint8, etc.
- Fix let statement lowering for pointer types (*char8 → int* bug)
- Fix PrintInt ABI mismatch (int64_t → int in io.c)
- Fix Makefile test bug (_test_tmp_pkg already exists)

Documentation:
- Rewrite README.md with features, examples, project structure
- Add docs/LanguageRef.md — complete language reference
- Add docs/Stdlib.md — standard library documentation
- Add docs/BuildAndTest.md — build and test guide

New examples: strings, map, result_option, try_operator (13 total)

examples/map.bux

@@ -0,0 +1,44 @@
+// Map - Hash map with String keys and int values
+import Std::Io::{PrintLine, PrintInt};
+import Std::Map::{Map, Map_New, Map_Set, Map_Get, Map_Has, Map_Len};
+
+func Main() -> int {
+    let m: Map = Map_New(16);
+    
+    PrintLine("Map operations:");
+    
+    Map_Set(&m, "one", 1);
+    Map_Set(&m, "two", 2);
+    Map_Set(&m, "three", 3);
+    
+    PrintLine("Length:");
+    PrintInt(Map_Len(&m));
+    PrintLine("");
+    
+    PrintLine("Get 'one':");
+    PrintInt(Map_Get(&m, "one"));
+    PrintLine("");
+    
+    PrintLine("Get 'two':");
+    PrintInt(Map_Get(&m, "two"));
+    PrintLine("");
+    
+    PrintLine("Get 'three':");
+    PrintInt(Map_Get(&m, "three"));
+    PrintLine("");
+    
+    Map_Set(&m, "two", 22);
+    PrintLine("Updated 'two':");
+    PrintInt(Map_Get(&m, "two"));
+    PrintLine("");
+    
+    if Map_Has(&m, "one") {
+        PrintLine("Has 'one': yes");
+    }
+    
+    if !Map_Has(&m, "four") {
+        PrintLine("Has 'four': no");
+    }
+    
+    return 0;
+}