[6s] Break out builtin commands into a list of structs

The 6s builtin commands are now in a separate file, with a list of name,
description, and function pointers.

src/user/6s/commands.cpp

@@ -0,0 +1,35 @@
+#include <edit/line.h>
+#include <util/format.h>
+#include "commands.h"
+
+static void
+help(edit::source &s)
+{
+    for (unsigned i = 0; i < g_builtins_count; ++i) {
+        char line[100];
+        util::counted<char> output { line, sizeof(line) };
+
+        builtin &cmd = g_builtins[i];
+
+        size_t len = util::format(output, "%20s - %s\r\n", cmd.name(), cmd.description());
+        s.write(line, len);
+    }
+}
+
+static void
+version(edit::source &s)
+{
+    static const char *gv = GIT_VERSION;
+
+    char line[100];
+    util::counted<char> output { line, sizeof(line) };
+
+    size_t len = util::format(output, "jsix version %s\r\n", gv);
+    s.write(line, len);
+}
+
+builtin g_builtins[] = {
+    { "help",       "list availble commands",               help },
+    { "version",    "print current jsix version",           version },
+};
+size_t g_builtins_count = sizeof(g_builtins) / sizeof(g_builtins[0]);