Add some utility fonctions

Two new helper functions have added to help in the setup of the
colorscheme.

- hsv2rgb: This 1st function generate the RGB hexadecimal string
           associated to a color given its HSV triplet.

- HL: This 2nd function is a wrapper for the 'highlight' command.

colors/odyssey.vim

@@ -18,6 +18,51 @@
 " Bootstrap {{{
 " }}}
 " Utilities {{{
+function! s:hsv2hex(hue, saturation, value)
+  let l:s = a:saturation / 100.0
+  let l:v = a:value / 100.0
+
+  let l:c = l:v * l:s
+  let l:h = a:hue / 60.0
+  let l:x = l:c * (1.0 - abs(fmod(l:h, 2) - 1.0))
+
+  if 0 <= l:h && l:h <= 1
+    let l:l = [l:c, l:x, 0.0]
+  elseif 1 < l:h && l:h <= 2
+    let l:l = [l:x, l:c, 0.0]
+  elseif 2 < l:h && l:h <= 3
+    let l:l = [0.0, l:c, l:x]
+  elseif 3 < l:h && l:h <= 4
+    let l:l = [0.0, l:x, l:c]
+  elseif 4 < l:h && l:h <= 5
+    let l:l = [l:x, 0.0, l:c]
+  elseif 5 < l:h && l:h <= 6
+    let l:l = [l:c, 0.0, l:x]
+  endif
+
+  let l:m = l:v - l:c
+
+  let l:l = [l:l[0] + l:m, l:l[1] + l:m, l:l[2] + l:m]
+  let l:l = [l:l[0] * 255, l:l[1] * 255, l:l[2] * 255]
+  let l:l = [round(l:l[0]), round(l:l[1]), round(l:l[2])]
+  let l:l = [float2nr(l:l[0]), float2nr(l:l[1]), float2nr(l:l[2])]
+
+  let l:f = "%02x"
+  return printf(l:f, l:l[0]) . printf(l:f, l:l[0]) . printf(l:f, l:l[0])
+endfunction
+
+function! s:HL(group, bg, ...)
+  let cbg = get(s:colors, a:bg)
+  let histring = 'highlight ' . a:group . ' ' . 'guibg=#'. cbg
+
+  if a:0 > 0
+    let cfg = get(s:colors, a:1)
+    let histring .= ' guifg=#'. cfg
+  endif
+
+  let histring .= ' cterm=none'
+  execute histring
+endfunction
 " }}}
 " Colors {{{
 " }}}