Recipient files, and a bag of goodies

Recipient files. You can now use the -R flag to pass the path to a file which contains one or more recipients, one per line. Empty lines and lines starting with # are ignored. This is compatible with SSH .pub files and most authorized_keys files.

--armor performance. Armored encoding is now up to 20x faster.

Various goodies. You can use -R - and -i - to read those files from standard input. Both age and age-keygen support a -version flag. We avoid leaving behind an empty output file when an error occurs. Output is not buffered if the input is not a TTY. Error messages and docs were improved. Release binaries are again available.