loader
------

- write doc

modutils
--------

Review extensively.
- Renaming:
    \luatexUseModule
    \luatexRequireModule
    \luatexModuleError
- stop using module() inside functions
- logic (see what LaTeX2e does)

mcallbacks
----------

Review extensively.
Compatibility : tex.luaversion not available in 0.25.4 :'(
Incorporate remaining bits from luatextra?