Add rudimentary map docs with tile descriptions from @AtomicChicken

Based on http://www.bay12forums.com/smf/index.php?topic=164123.msg8158676#msg8158676

docs/Lua API.rst

@@ -1414,6 +1414,8 @@ Items module
 
   Checks whether the item is assigned to a squad.
 
+.. _lua-maps:
+
 Maps module
 -----------
 

docs/api/Maps.rst

@@ -0,0 +1,59 @@
+.. include:: <isonum.txt>
+
+========
+Maps API
+========
+
+DFHack offers several ways to access and manipulate map data.
+
+* C++: the ``Maps`` and ``MapCache`` modules
+* Lua: the `dfhack.maps module <lua-maps>`_
+* All languages: the ``map`` field of the ``world`` global contains raw map data
+  when the world is loaded.
+
+.. note::
+
+    This page will eventually go into more detail about the available APIs.
+    For now, it is just an overview of how DF map data is structured.
+
+.. contents:: Contents
+    :local:
+
+Tiles
+=====
+
+The DF map has several types of tiles:
+
+- **Local tiles** are at the smallest scale. In regular fortress/adventure mode
+  play, the cursor takes up 1 local tile.
+
+  Objects that use local tile coordinates include:
+
+  - Units
+  - Items
+  - Projectiles
+
+- **Blocks** are 16 |times| 16 |times| 1 groups of local tiles. Internally, many
+  tile details are stored at the block level for space-efficiency reasons.
+  Blocks are visible during zoomed-in fast travel in adventure mode.
+
+  Objects that use block coordinates include:
+
+  - Armies
+
+- **Region tiles** are 3 |times| 3 groups of columns of blocks (they span the
+  entire z-axis), or 48 |times| 48 columns of local tiles. DF sometimes refers
+  to these as "mid-level tiles" (MLTs). Region tiles are visible when resizing
+  a fortress before embarking, or in zoomed-out fast travel in adventure mode.
+
+- **World tiles** are
+
+  - 16 |times| 16 groups of region tiles, or
+  - 48 |times| 48 groups of columns of blocks, or
+  - 768 |times| 768 groups of columns of local tiles
+
+  World tiles are visible on the world map before embarking, as well as in the
+  civilization map in fortress mode and the quest log in adventure mode.
+
+- Some map features are stored in 16 |times| 16 groups of world tiles, sometimes
+  referred to as "feature shells".

docs/api/index.rst

@@ -0,0 +1,8 @@
+====================
+DFHack API Reference
+====================
+
+.. toctree::
+    :maxdepth: 1
+
+    /docs/api/Maps

docs/index-dev.rst

@@ -13,6 +13,7 @@ These are pages relevant to people developing for DFHack.
    /docs/NEWS-dev
    /docs/Lua API
    /docs/Remote
+   /docs/api/index
    /docs/Documentation
    /docs/Structures-intro
    /docs/Memory-research