[ADD] explanation + interaction of journals + chart of accounts

After discussion with fp this probably isn't the direction (ish), but
want to checkpoint this in order to work on other stuff earlier in the
document, but not commit a single gigantic blob of stuff.

_static/atom.js

@@ -0,0 +1,48 @@
+function createAtom(val, options) {
+    var watchers = {};
+    var validator = options && options.validator || function () { return true; };
+
+    function transition(next) {
+        if (!validator(next)) {
+            var err = new Error(next + " failed validation");
+            err.name = "AssertionError";
+            throw err;
+        }
+
+        var prev = val;
+        val = next;
+
+        Object.keys(watchers).forEach(function (k) {
+            watchers[k](k, atom, prev, next);
+        });
+    }
+
+    var atom = {
+        addWatch: function (key, fn) {
+            watchers[key] = fn;
+        },
+
+        removeWatch: function (key) {
+            delete watchers[key];
+        },
+
+        swap: function (fn) {
+            var args = [val].concat([].slice.call(arguments, 1));
+            transition(fn.apply(null, args));
+        },
+
+        reset: function (v) {
+            transition(v);
+        },
+
+        deref: function () {
+            return val;
+        },
+
+        toString: function () {
+            return "Atom(" + JSON.stringify(val) + ")";
+        }
+    };
+
+    return atom;
+}