[lltx] [luatexbase] Allocating attributes from lua

[Manuel Pégourié-Gonnard]

Hi,

I just implemented the following:

- <number> luatexbase.new_attribute(<string> name, <any type> silent = nil)
Allocates a new attribute, without associated TeX CS, and returns the allocated
number. If an error occurs, call error() in silent is false (default) or return
-1 (error handling up to the caller) is silent is true.

- luatexbase.unset_attribute(<string> name)
Unsets the named attribute.

I changed the TeX macros to be wrappers around these functions.

I hope it's what you asked for, otherwise please complain :-)

Manuel.