fix: multi-arg calls, uninitialized symbols, param limit; add banner img; update docs

- Fix segfault from uninitialized Symbol structs in scope/hir_lower/sema
- Fix null ReadFile crash in Cli_MergeFileInto (missing stdlib files)
- Extend function params from 6 to 9 (bux_str_format needs 9 args)
- Add ExprList/HirArgList linked lists for >2 call arguments
- Add banner image to README
- Update docs: C backend is now primary (not QBE)

src_bux/scope.bux

@@ -72,7 +72,7 @@ func Scope_Lookup(scope: *Scope, name: String) -> Symbol {
         }
         cur = cur.parent;
     }
-    var empty: Symbol;
+    var empty: Symbol = Symbol { kind: 0, name: "", typeKind: 0, typeName: "", isMutable: false, isPublic: false, decl: null as *Decl };
     return empty;
 }
 
@@ -84,7 +84,7 @@ func Scope_LookupLocal(scope: *Scope, name: String) -> Symbol {
         }
         i = i + 1;
     }
-    var empty: Symbol;
+    var empty: Symbol = Symbol { kind: 0, name: "", typeKind: 0, typeName: "", isMutable: false, isPublic: false, decl: null as *Decl };
     return empty;
 }