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/try_operator.bux

@@ -0,0 +1,58 @@
+// Try operator ? - Error propagation
+import Std::Io::{PrintLine, PrintInt};
+
+enum Result {
+    Ok(int),
+    Err(String)
+}
+
+func Result_NewOk(value: int) -> Result {
+    let r: Result = Result { tag: Result_Ok };
+    r.data.Ok_0 = value;
+    return r;
+}
+
+func Result_NewErr(msg: String) -> Result {
+    let r: Result = Result { tag: Result_Err };
+    r.data.Err_0 = msg;
+    return r;
+}
+
+func Divide(a: int, b: int) -> Result {
+    if b == 0 {
+        return Result_NewErr("division by zero");
+    }
+    return Result_NewOk(a / b);
+}
+
+func Compute() -> Result {
+    let x: int = Divide(10, 2)?;
+    let y: int = Divide(x, 5)?;
+    return Result_NewOk(y);
+}
+
+func ComputeWithError() -> Result {
+    let x: int = Divide(10, 0)?;
+    let y: int = Divide(x, 5)?;
+    return Result_NewOk(y);
+}
+
+func Main() -> int {
+    PrintLine("Try operator demo:");
+    
+    let r1: Result = Compute();
+    if r1.tag == Result_Ok {
+        PrintLine("Compute() = ");
+        PrintInt(r1.data.Ok_0);
+        PrintLine("");
+    } else {
+        PrintLine("Compute() failed");
+    }
+    
+    let r2: Result = ComputeWithError();
+    if r2.tag == Result_Err {
+        PrintLine("ComputeWithError() failed as expected");
+    }
+    
+    return 0;
+}