Develop how to load files in packages and use it for handling hyphenation dictionaries

[gfngfn]

As a first step toward loading local files in packages, we introduce a very straightforward mechanism, here : string, for referring to the directory of the source file.

• Add token here
• Add base type hyphenation
• Add primitive set-hyphenation-dictionary : hyphenation -> context -> context
• Add primitive load-hyphenation-dictionary : string -> hyphenation
• Create package hyph-english and migrate english.satysfi-hyph to it
• Remove the hardcoded loading operation of english.satysfi-hyph from satysfi
• Register hyph-english to the package registry
• Make document classes use hyph-english
• Register document classes to the package registry