Terminal color tweaks. (#201)

* Add KiTTY configuration (manually; could potentially use
  https://github.com/stayradiated/termcolors/pull/17/ in the future)
* Tweak foreground/background/white/black colors to be visually distinct
  from one another

Closes #200.

build/templates/One Dark.Xresources

@@ -4,8 +4,8 @@
 *.cursorColor:  <%=white.gui%>
 
 ! black
-*.color0:       <%=black.gui%>
-*.color8:       <%=visual_grey.gui%>
+*.color0:       <%=comment_grey.gui%>
+*.color8:       <%=gutter_fg_grey.gui%>
 
 ! red
 *.color1:       <%=red.gui%>
@@ -33,5 +33,5 @@
 
 ! white
 *.color7:       <%=white.gui%>
-*.color15:      <%=comment_grey.gui%>
+*.color15:      <%=visual_grey.gui%>