[spectrum] Delete submodule

The following was introduced in zsh 5.0:

> %F, %K, %f, %k allow colouring of prompts both using ANSI colour names
  and values supported by individual terminal emulators.

making this submodule obsolete.

See http://zsh.sourceforge.net/releases.html

Closes #224

modules/spectrum/README.md

@@ -1,8 +0,0 @@
-Spectrum
-========
-
-Provides initialization for easy 256 colours and effects.
-
-See [a guide to 256 color codes](http://lucentbeing.com/writing/archives/a-guide-to-256-color-codes/), in particular, the "Spectrum, a ZSH Abstraction" section.
-
-

modules/spectrum/init.zsh

@@ -1,39 +0,0 @@
-#
-# Provides for easier use of 256 colors and effects.
-#
-
-# Return if requirements are not found.
-if [[ ${TERM} == 'dumb' ]]; then
-  return 1
-elif
-  [[ -n ${FX} ]]; then
-  # FX is set or sourced by another module
-  return 1
-fi
-
-typeset -gA FX FG BG
-
-FX=(
-                                        reset                        "\e[00m"
-                                        normal                       "\e[22m"
-  bold                      "\e[01m"    no-bold                      "\e[22m"
-  italic                    "\e[03m"    no-italic                    "\e[23m"
-  underline                 "\e[04m"    no-underline                 "\e[24m"
-  blink                     "\e[05m"    no-blink                     "\e[25m"
-  reverse                   "\e[07m"    no-reverse                   "\e[27m"
-)
-
-FG[none]="${FX[none]}"
-BG[none]="${FX[none]}"
-colors=(black red green yellow blue magenta cyan white)
-for color in {0..255}; do
-  if (( ${color} >= 0 )) && (( ${color} < ${#colors} )); then
-    index=$(( ${color} + 1 ))
-    FG[${colors[${index}]}]="\e[38;5;${color}m"
-    BG[${colors[${index}]}]="\e[48;5;${color}m"
-  fi
-
-  FG[${color}]="\e[38;5;${color}m"
-  BG[${color}]="\e[48;5;${color}m"
-done
-unset color{s,} index