fix .gitignore file and add commit missing std lib file

.gitignore

@@ -10,6 +10,6 @@
 # -andrewrk
 
 zig-cache/
-build/
-build-*/
-docgen_tmp/
+/build/
+/build-*/
+/docgen_tmp/

std/build/fmt.zig

@@ -0,0 +1,35 @@
+const std = @import("../index.zig");
+const build = @import("../build.zig");
+const Step = build.Step;
+const Builder = build.Builder;
+const BufMap = std.BufMap;
+const mem = std.mem;
+
+pub const FmtStep = struct {
+    step: Step,
+    builder: *Builder,
+    argv: [][]const u8,
+
+    pub fn create(builder: *Builder, paths: []const []const u8) *FmtStep {
+        const self = builder.allocator.create(FmtStep) catch unreachable;
+        const name = "zig fmt";
+        self.* = FmtStep{
+            .step = Step.init(name, builder.allocator, make),
+            .builder = builder,
+            .argv = builder.allocator.alloc([]u8, paths.len + 2) catch unreachable,
+        };
+
+        self.argv[0] = builder.zig_exe;
+        self.argv[1] = "fmt";
+        for (paths) |path, i| {
+            self.argv[2 + i] = builder.pathFromRoot(path);
+        }
+        return self;
+    }
+
+    fn make(step: *Step) !void {
+        const self = @fieldParentPtr(FmtStep, "step", step);
+
+        return self.builder.spawnChild(self.argv);
+    }
+};