attr: \newluatexattribute -> \newattribute

all: error if not running luatex!

modutils
--------

- Renaming:
    \luatexUseModule
    \luatexRequireModule
- syntax of public TeX macros and Lua functions
- create private functions for infwarrerr?
- use tex.error for error reporting if available
- review logic (see what LaTeX2e does)
- General review of code and comments.
- Update user documentation. Include template(s) for Lua modules.

mcb
---

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


afterwards
----------

- Bump version number, upload.