Added module system to changelog, commands, and hooks doc files

doc/pages/changelog.asciidoc

@@ -15,6 +15,13 @@ released versions.
 * `edit -scratch` with no buffer name will create a new
   scratch buffer with a unique autogenerated name.
 
+* Introduced a module system using the `provides-module` and
+  `requires-module` commands that allows for lazily loading language
+  support files with dependency resolution.
+
+* Added a new hook `ModuleLoad` which is run when a module is loaded, as
+  now options needed by modules aren't defined until the module is loaded.
+
 == Kakoune 2019.01.20
 
 * `auto_complete` has been renamed to `autocomplete` for more

doc/pages/commands.asciidoc

@@ -312,6 +312,15 @@ but not really useful in that context.
 *debug* {info,buffers,options,memory,shared-strings,profile-hash-maps,faces,mappings}::
     print some debug information in the *\*debug** buffer
 
+== Module commands
+
+*provide-module* [<switches>] <name> <commands>::
+    declares a new module that is provided by the given commands. The commands
+    passed into the module are guaranteed to be run only once.
+
+*require-module* <name>::
+    guarantees the <name> module is loaded before continuing command execution
+
 == Multiple commands
 
 Commands (c.f. previous sections) can be chained, by being separated either

doc/pages/hooks.asciidoc

@@ -180,6 +180,9 @@ name. Hooks with no description will always use an empty string.
 *RawKey* `key`::
     Triggered whenever a key is pressed by the user
 
+*ModuleLoad* `module`::
+    Triggered when a module is loaded
+
 Note that some hooks will not consider underlying scopes depending on what
 context they are bound to be run into, e.g. the `BufWritePost` hook is a buffer
 hook, and will not consider the `window` scope.