Refactor to clarify wording around positional info

Previously, position and location were used interchangably, and
confusingly.  This commit drops the “location” term, uses “position”
and “positional info” for the thing at `node.position`, and uses
“point” for the thing at `position.start` and `position.end`.

Closes GH-13.

Author: wooorm

readme.md

@@ -44,7 +44,7 @@ See [**nlcst**][nlcst] for more information on **retext** nodes,
 
 A Node represents any unit in the Unist hierarchy.  It is an abstract
 interface.  Interfaces extending **Node** must have a `type` property,
-and may have `data` or `location` properties.  `type`s are defined by
+and may have `data` or `position` properties.  `type`s are defined by
 their namespace.
 
 Subsets of Unist are allowed to define properties on interfaces which
@@ -55,7 +55,7 @@ extend Unist’s abstract interfaces.  For example, [mdast][] defines
 interface Node {
   type: string;
   data: Data?;
-  position: Location?;
+  position: Position?;
 }
 ```
 
@@ -70,32 +70,32 @@ compiled HTML element.
 interface Data { }
 ```
 
-#### `Location`
+#### `Position`
 
-**Location** references a range consisting of two points in a [Unist
-file][file].  **Location** consists of a `start` and `end` position.
+**Position** references a range consisting of two points in a [Unist
+file][file].  **Position** consists of a `start` and `end` point.
 And, if relevant, an `indent` property.
 
 When the value represented by a node is not present in the document
 corresponding to the syntax tree at the time of reading, it must not
-have a location.  These nodes are said to be _generated_.
+have positional information.  These nodes are said to be _generated_.
 
 ```idl
-interface Location {
-  start: Position;
-  end: Position;
+interface Position {
+  start: Point;
+  end: Point;
   indent: [uint32 >= 1]?;
 }
 ```
 
-#### `Position`
+#### `Point`
 
-**Position** references a point consisting of two indices in a
+**Point** references a point consisting of two indices in a
 [Unist file][file]: `line` and `column`, set to 1-based integers.  An
 `offset` (0-based) may be used.
 
 ```idl
-interface Position {
+interface Point {
   line: uint32 >= 1;
   column: uint32 >= 1;
   offset: uint32 >= 0?;
@@ -148,9 +148,9 @@ A list of **vfile**-related utilities can be found at [**vfile**][vfile].
 *   [`unist-util-find-after`](https://github.com/syntax-tree/unist-util-find-after)
     — Find a node after another node
 *   [`unist-util-find-all-after`](https://github.com/syntax-tree/unist-util-find-all-after)
-    — Find nodes after another node or position
+    — Find nodes after another node or index
 *   [`unist-util-find-all-before`](https://github.com/syntax-tree/unist-util-find-all-before)
-    — Find nodes before another node or position
+    — Find nodes before another node or index
 *   [`unist-util-find-all-between`](https://github.com/mrzmmr/unist-util-find-all-between)
     — Find nodes between two nodes or positions
 *   [`unist-util-find-before`](https://github.com/syntax-tree/unist-util-find-before)
@@ -170,17 +170,17 @@ A list of **vfile**-related utilities can be found at [**vfile**][vfile].
 *   [`unist-util-parents`](https://github.com/eush77/unist-util-parents)
     — `parent` references on nodes
 *   [`unist-util-position`](https://github.com/syntax-tree/unist-util-position)
-    — Get the position of nodes
+    — Get positional info of nodes
 *   [`unist-util-remove`](https://github.com/eush77/unist-util-remove)
     — Remove nodes from Unist trees
 *   [`unist-util-remove-position`](https://github.com/syntax-tree/unist-util-remove-position)
-    — Remove `position`s from a unist tree
+    — Remove positional info from a unist tree
 *   [`unist-util-select`](https://github.com/eush77/unist-util-select)
     — Select nodes with CSS-like selectors
 *   [`unist-util-source`](https://github.com/syntax-tree/unist-util-source)
-    — Get the source of a value (node, location)
+    — Get the source of a value (node or position) in a file
 *   [`unist-util-stringify-position`](https://github.com/syntax-tree/unist-util-stringify-position)
-    — Stringify a node, location, or position
+    — Stringify a node, position, or point
 *   [`unist-util-visit`](https://github.com/syntax-tree/unist-util-visit)
     — Recursively walk over nodes
 *   [`unist-util-visit-parents`](https://github.com/syntax-tree/unist-util-visit-parents)