CLI: Improved auto-completion behavior

Auto-complete keywords (for, where, filter, ...) and symbol names (names
of protocols, tables, ...). Client can request daemon for list of all
symbols using new cli command `refresh symbols`.

Next changes:
  - Behavior is configured by *.Y files using flags CLI_SF_*
  - The file doc/reply_codes was moved to header file
    client/reply_codes.h.
  - Share birdcl input_read() function code for birdc non-interactive
    mode.
  - BIRD daemon notifies the client about new symbol set.
  - BIRD pushes notification to the client about new symbol set and then
    the client should request a package with all symbols (`refresh
    symbols`).
  - File-based history of previous commands(). In interactive mode in
    birdc is stored history of all commands in ~/.birdc_history file.
  - BIRD daemon sends notification to clients about interface updates
  - Maintains a list of all connected cli clients to daemon. Daemon
    sends to all cli clients notification about interfaces states up and
    down.