templatefilters: drop callable support from json() This backs out ae5447de4c11. A callable should be evaluated beforehand by templater.runsymbol().

ui: use bytes IO and convert EOL manually in ui.editor() Text IO sucks on Python 3 as it must be a unicode stream. We could introduce a wrapper that converts unicode back to bytes, but it wouldn't be simple to handle offsets transparently from/to underlying IOBase API. Fortunately, we don't need to process huge text files, so let's stick to bytes IO and convert EOL in memory.

util: add helper to convert between LF and native EOL See the next patch for why.

util: extract pure tolf/tocrlf() functions from eol extension This can be used for EOL conversion of text files.