v0.3.0: restructure directories

- src/        ← compiler/selfhost/  (canonical Bux compiler)
- bootstrap/  ← compiler/bootstrap/ (Nim bootstrap)
- lib/        ← library/std/        (standard library)
- rt/         ← library/runtime/    (C runtime)
- tests/      ← compiler/tests/     (unit tests)
- Remove _selfhost/ (built into build/selfhost/ now)
- Update all path references (Makefile, cli.nim, cli.bux, docs)
- Bump version to 0.3.0

lib/Array.bux

@@ -0,0 +1,44 @@
+module Std::Array {
+
+extern func bux_alloc(size: uint) -> *void;
+extern func bux_realloc(ptr: *void, size: uint) -> *void;
+extern func bux_free(ptr: *void);
+extern func bux_bounds_check(index: uint, len: uint);
+
+struct Array<T> {
+    data: *T,
+    len: uint,
+    cap: uint,
+}
+
+func Array_New<T>(cap: uint) -> Array<T> {
+    let data = bux_alloc(cap * sizeof(T)) as *T;
+    return Array<T> { data: data, len: 0, cap: cap };
+}
+
+func Array_Push<T>(self: *Array<T>, value: T) {
+    if self.len >= self.cap {
+        self.cap = self.cap * 2;
+        self.data = bux_realloc(self.data as *void, self.cap * sizeof(T)) as *T;
+    }
+    self.data[self.len] = value;
+    self.len = self.len + 1;
+}
+
+func Array_Get<T>(self: *Array<T>, index: uint) -> T {
+    bux_bounds_check(index, self.len);
+    return self.data[index];
+}
+
+func Array_Len<T>(self: *Array<T>) -> uint {
+    return self.len;
+}
+
+func Array_Free<T>(self: *Array<T>) {
+    bux_free(self.data as *void);
+    self.data = null as *T;
+    self.len = 0;
+    self.cap = 0;
+}
+
+}