v0.17.0rc1

• configuration files are now saved to ~/.config/elinks/ or $XDG_CONFIG_HOME/elinks/ #199
  User must copy files from ~/.elinks/ to ~/.config/elinks/ himself or herself
• HOME_ETC support was dropped, you can set ELINKS_CONFDIR instead
• idn2 in place of idn #206
• libcss support (a few netsurf's libraries are required). Set document.css.libcss = 1 to enable
• experimental libsixel support (image/*; img2sixel %s; copiousoutput) in ~/.mailcap
  Must be enabled in a few places in configuration: set document.plain.sixel = 1
  and in terminal options. Do not try it on metered remote connections
• testing libcurl support (explicit FTPS and SFTP among others)
  To enable set protocol.ftp.use_curl = 1
  set protocol.http.use_curl = 1 for http/https
• ui.sessions.postpone_unlink option. Delete temporary files at exit instead of immediately after
  closing viewer #257
• redefined isspace #249
• Serbian translation update
• compilation fixes