Log Message:
news/flnews: Update to 0.18

- Searching for Unicode string in current article is now supported (case
  insensitive variant based on Unicode case folding algorithm)
- Unicode database updated to version 13.0.0 (CaseFolding.txt added)
- The new 'force_unicode' entry in configfile set to a nonzero value sends
  all outgoing articles in Unicode, if they contain non-ASCII characters
- Dark background color is now usable
- MIME conformance reached (as defined in RFC 2049 Section 2)
- If selected text is present, quote only selected text for followup
- XDG desktop entry and icon theme added (option CFG_XDG_DISABLE)
- Configuration window in GUI now allows to disable the "User-Agent" header
  field for outgoing articles
- It is now possible to enable AUTHINFO USER/PASS without encrypted connection
  (option CFG_NNTP_AUTH_UNENCRYPTED)
  This allows to use stunnel instead of the internal TLS module
- TLS module no longer calls deprecated functions HMAC*(), RSA_size() and
  SSL_get_peer_certificate() for OpenSSL API 3.0.0