Numeric escapes in strings get double backslashes

[Zash]

A string like

local x = "hello\0\1\2world\n\10"

turns into

local x = "hello\\0\\1\\2world\n\\10"

[Zash]

The problem seems to be fix_str() in typedlua/tlcode.lua and/or typedlua/tllexer.lua.