Implement ^,$ navigating to 0%,100% in x-direction

This is made possible by also allowing the second
argument to be "x" or "y". We supply "y" as the
default to retain the current, more commonly
desired behavior.

src/config.ts

@@ -44,6 +44,9 @@ const DEFAULTS = o({
         "l": "scrollpx 50",
         "G": "scrollto 100",
         "gg": "scrollto 0",
+        "$": "scrollto 100 x",
+        // "0": "scrollto 0 x", // will get interpreted as a count
+        "^": "scrollto 0 x",
         "H": "back",
         "L": "forward",
         "d": "tabclose",

src/excmds.ts

@@ -186,21 +186,25 @@ export function scrollpx(a: number, b: number) {
     window.scrollBy(a, b)
 }
 
-/** If one argument is given, scroll to that percentage down the page.
-    If two arguments are given, treat as x and y values to give to window.scrollTo
+/** If two numbers are given, treat as x and y values to give to window.scrollTo
+    If one number is given, scroll to that percentage along a chosen axis,
+        defaulting to the y-axis
 */
 //#content
-export function scrollto(a: number, b?: number) {
+export function scrollto(a: number, b: number | "x" | "y" = "y") {
     a = Number(a)
-    // if b is undefined, Number(b) is NaN.
-    b = Number(b)
+    if (b === "y") {
         window.scrollTo(
-        b ? a : window.scrollX,
-        b
-            ? b
-            : a.clamp(0, 100) *
-              (window.document.scrollingElement.scrollHeight / 100)
-    )
+            window.scrollX,
+            a.clamp(0, 100) * window.document.scrollingElement.scrollHeight / 100)
+    }
+    else if (b === "x") {
+        window.scrollTo(
+            a.clamp(0, 100) * window.document.scrollingElement.scrollWidth / 100,
+            window.scrollY)
+    } else {
+        window.scrollTo(a, Number(b)) // a,b numbers
+    }
 }
 
 //#content