Fix usages of global variables

- Lint references to unknown fields of modules, excluding the keys and
   colours modules. This caught several silly errors in our stub files,
   but nothing else.
 - Lint on using unknown globals. This highlighted a couple of really
   silly mistakes. Fixes #427.
 - Add documentation for fs.attributes, fs.getCapacity and pocket, as
   they were not defined before.

Co-authored-by: JackMacWindows <jackmacwindowslinux@gmail.com>

doc/stub/fs.lua

@@ -19,6 +19,36 @@ function getFreeSpace(path) end
 function find(pattern) end
 function getDir(path) end
 
+--- Get the capacity of the drive at the given path.
+--
+-- This may be used in conjunction with @{getFreeSpace} to determine what
+-- percentage of this drive has been used.
+--
+-- @tparam string path The path of the drive to get.
+-- @treturn number This drive's capacity. This will be 0 for "read-only" drives,
+-- such as the ROM or treasure disks.
+function getCapacity(path) end
+
+--- Get attributes about a specific file or folder.
+--
+-- The returned attributes table contains information about the size of the
+-- file, whether it is a directory, and when it was created and last modified.
+--
+-- The creation and modification times are given as the number of milliseconds
+-- since the UNIX epoch. This may be given to @{os.date} in order to convert it
+-- to more usable form.
+--
+-- @tparam string path The path to get attributes for.
+-- @treturn { size = number, isDir = boolean, created = number, modified = number }
+-- The resulting attributes.
+-- @throws If the path does not exist.
+-- @see getSize If you only care about the file's size.
+-- @see isDir If you only care whether a path is a directory or not.
+function attributes(path) end
+
+-- Defined in bios.lua
+function complete(sPath, sLocation, bIncludeFiles, bIncludeDirs) end
+
 --- A file handle which can be read from.
 --
 -- @type ReadHandle