attr: \newluatexattribute -> \newattribute

modutils
--------

- Renaming:
    \luatexUseModule
    \luatexRequireModule
- syntax of public TeX macros and Lua functions
- create private functions for infwarrerr?
- review logic (see what LaTeX2e does)
- General review of code and comments.
- Update user documentation.

mcb
---

- Incorporate remaining bits from luatextra?
- Enhance test file?
- General review of code and comments.
- Update user documentation.

afterwards
----------

- Bump version number, upload.
