v0.4.0: selfhost loop progress

- Fix stdlib merge: merge ALL lib/*.bux via bux_list_dir (was 0)
- Fix Cli_FindStdlibDir: search for lib/ not stdlib/
- Fix stdlib path: remove Std/ subdir (now flat in lib/)
- Fix runtime paths: add ../../ fallback for build/selfhost depth
- Remove hardcoded /home/ziko paths from src/cli.bux
- Fix Json.bux: avoid var-in-if-block scoping bug (5 errors)
- Add improved sema error messages (reverted due to crash)
- Remaining: 2 parserParsePostfix sema forward-ref errors
- Update PLAN.md with v0.3.0-v1.0.0 roadmap

src/cli.bux

@@ -149,10 +149,10 @@ func Cli_Build(srcPath: String, outPath: String) -> int {
         ioPath = "../rt/io.c";
     }
     if !FileExists(rtPath) {
-        rtPath = "/home/ziko/z-git/bux/bux/rt/runtime.c";
+        rtPath = "../../rt/runtime.c";
     }
     if !FileExists(ioPath) {
-        ioPath = "/home/ziko/z-git/bux/bux/rt/io.c";
+        ioPath = "../../rt/io.c";
     }
 
     // Compile with cc
@@ -298,7 +298,7 @@ func Cli_FindStdlibDir(projectDir: String) -> String {
     if DirExists(path) { return path; }
     path = bux_path_join(projectDir, "../lib");
     if DirExists(path) { return path; }
-    path = "/home/ziko/z-git/bux/bux/lib";
+    path = bux_path_join(projectDir, "../../lib");
     if DirExists(path) { return path; }
     return "";
 }