Fix with_channel_from_string for long strings that do not fit in pipe, by using a thread for outputing the string.
Some minor optimizations, using the fact that re-raising an exception preserves the backtrace and the constraint on OCaml version (>=4.03) ensures that match-with-exception is available.
2021-09-24, version 0.2.0
Add string_of_channel, add_file and string_of_file.