rename row to $row in docs and comments

Author: Gudine

docs/docs/data/blocks.md

@@ -25,7 +25,7 @@ Inline fields on blocks can be loaded using the [field syntax](fields):
 ```js
 // In queries and expressions, you can just reference the field directly:
 @block and genre = "Fantasy"
-@block and row["last reviewed"] > date(now) - dur(7d)
+@block and $row["last reviewed"] > date(now) - dur(7d)
 
 // In javascript, use the field API:
 block.value("last reviewed")

docs/docs/data/fields.md

@@ -25,8 +25,8 @@ You can reference fields directly by name in queries and datacore expressions. T
 // You can also reference intrinsic fields (fields prefixed with `$`):
 @block and $tags.contains("#test")
 
-// Use the implicit 'row' in order to handle fields with spaces in their names:
-@section and row["last reviewed"] >= date(now) - dur(7d)
+// Use the implicit '$row' in order to handle fields with spaces in their names:
+@section and $row["last reviewed"] >= date(now) - dur(7d)
 ```
 
 ## In Javascript

docs/docs/data/pages.md

@@ -35,7 +35,7 @@ You can reference page fields in queries and expressions directly by case-insens
 
 ```js
 @page and rating >= 7
-@page and row["spaced field"].contains("thing")
+@page and $row["spaced field"].contains("thing")
 ```
 
 ## In Javascript

docs/docs/data/sections.md

@@ -26,7 +26,7 @@ Inline fields on sections can be loaded using the [field syntax](fields):
 
 ```js
 // In queries and expressions, you can just reference the field directly:
-@section and row["last reviewed"] > date(now) - dur(7d)
+@section and $row["last reviewed"] > date(now) - dur(7d)
 
 // In javascript, use the field API:
 section.value("last reviewed")

src/expression/expression.ts

@@ -149,11 +149,11 @@ export namespace Expressions {
         return op == "<=" || op == "<" || op == ">" || op == ">=" || op == "!=" || op == "=";
     }
 
-    /** Returns a set of all unbound variables (i.e., variables not provided by `row`, lambdas, or similar.) */
+    /** Returns a set of all unbound variables (i.e., variables not provided by `$row`, lambdas, or similar.) */
     export function unboundVariables(expr: Expression, bound: Set<string> = new Set([ROW])): Set<string> {
         switch (expr.type) {
             case "binaryop":
-                // Special case `row["...."]`.
+                // Special case `$row["...."]`.
                 if (
                     expr.op === "index" &&
                     expr.left.type == "variable" &&