[letterspace] split long line
[extralibs] remove references to typo-krn.lua and related functionality
[letterspace] remove typo-krn.lua
[letterspace] purge redundant locals
[doc] update news
[letterspace] merge luaotfload-extralibs into luaotfload-letterspace
[extralibs] kill luaotfload-extralibs.lua
[letterspace] eliminate some now unnecessary globals