Xresources: use my old version

This is my old version of Xresources that I configured for xterm.  I plan to
move to gnome-terminal or xfce4-terminal, but I'm saving this for posterity.
zshenv: refactor 256-color support; export TERM

* use a case statement to allow for pattern matching
* export TERM
zshenv: add 256-color support for xfce4-terminal
zshenv: skip_global_compinit for Ubuntu

This fixes the noticably slow (300ms) startup time on Ubuntu.
set XDG Public share to $HOME

This gets reset automatically if ~/Public does not exist.
xfce4-terminal: add config file
xfce4-terminal: fix opaque cursor

There is a bug [1] since 2010 that xfce4-terminal draws the cursor as an
opaque color rather than using the "invert" style.  This means that it is
impossible to see what's under the cursor.  The workaround, as noted in [1],
is to manually set CursorColor to the empty string in the rc file.

[1] https://bugs.launchpad.net/ubuntu/+source/xfce4-terminal/+bug/673489
xfce4-terminal: switch to gray foreground

Previously, I used slategray3/slategray1 for foreground/bold, but I think
I like normal gray better.