import document module on-demand

This will save several megabytes of RAM when startup.

koreader-base

@@ -6,17 +6,11 @@ this replaces the former standalone binary which invoked the Lua interpreter/com
 now, we use the "default" interpreter/compiler
 ]]--
 
-require "libs/libkoreader-cre"
-require "libs/libkoreader-djvu"
 require "libs/libkoreader-input"
 require "libs/libkoreader-lfs"
-require "libs/libkoreader-pdf"
-require "libs/libkoreader-pic"
 require "libs/libkoreader-luagettext"
 
 -- libraries converted to FFI:
-KOPTContext = require("ffi/koptcontext")
-DrawContext = require("ffi/drawcontext")
 Blitbuffer = require("ffi/blitbuffer")
 freetype = require("ffi/freetype")
 Image = require("ffi/mupdfimg")