Terminfo fixes from neovim work

[Jonathan de Boyne Pollard]

This neovim work led me to do some further work on neovim.  neovim, if you are not familiar with it, attempts to do what it does in the "modern" way, from putting its per-user configuration files in $XDG_CONFIG_HOME/nvim to using terminfo and only terminfo.  As part of working on its textual user interface layer, I have constructed a list of terminfo modifications that you might like to consider:

• genuine Xterm (i.e. not something that lies about being xterm) supports DECSTBM, DECSLRM, and DECLRMM.  But xterm-new et al. terminal types in terminfo do not define any of set_bottom_margin_parm, set_top_margin_parm, set_left_margin_parm, set_right_margin_parm, set_lr_margin, or set_tb_margin.  
• The interix terminal type is missing a carriage_return entry.  Yes, it is CR on Interix.  (-:
• The screen terminal type is missing from_status_line and to_status_line.  The tmux entry uses the control sequences for setting the window title here.  The screen equivalents, per the screen manual page, are ESC k for "to" and ST (but only in its 7-bit guise as ESC \) for "from".
• Suckless Simpleterm is not the only terminal emulator that supports DECSCUSR and whose terminfo entry can benefit from Ss and Se.  Experimentation and source analysis has given me this list of terminal emulators that understand DECSCUSR:
• genuine Xterm
• iTerm2 (supports Xterm vertical bar extension)
• MinTTY 0.4.3-1 and later
• TeraTerm (supports Xterm vertical bar extension)
• libvte-based emulators since at least version 0.39
• screen
• rxvt-unicode (supports Xterm vertical bar extension)
• The entry for linux can have Ss=\x1b[?%?%p1%{2}%<%t%{8}%p1%{2}%=%t%{24}%p1%{3}%=%t%{1}%p1%{4}%=%t%{17}%p1%{5}%=%t%{1}%p1%{6}%=%t%{17}%e%{0}%;%dc, which is a complicated way of saying use CSI ? P1 c with 8, 8, 24, 1, 17, 1, and 17 as the parameter, and Se=\x1b[?c .
  
• In addition to Xterm, libvte since version 0.36 and iTerm2 both support SGR 38 and SGR 48 with colon-separated, rather than semicolon-separated, subparameters.

On the subject of Interix, please note that there are several other problems with the Interix entry, which have bothered me, an Interix user, for a while now.  (-: