[luatex] Font encoding

[Javier Múgica]

The files with the definitions for the different font encodings would
containg mappings from the utf-8 characters and a few control
sequences (like \SS) to the font encoding. A LaTeX like style would
look like

\catcode`Œ=\active   %If this is not itself contained in the next macro
\DeclareTextSymbol{Œ}{T1}{215}

A more direct approach would just be

\catcode`Œ=\active
\defŒ{\char215 }