move init code into new file, add section.

autoload/airline/section.vim

@@ -0,0 +1,47 @@
+" MIT License. Copyright (c) 2013 Bailey Ling.
+" vim: et ts=2 sts=2 sw=2
+
+function! s:get_val(key, append)
+  let val = ''
+  let part = airline#parts#get(a:key)
+  if exists('part.function')
+    let func = (part.function).'()'
+  elseif exists('part.text')
+    let func = '"'.(part.text).'"'
+  elseif exists('part.raw')
+    return part.raw
+  else
+    return a:key
+  endif
+
+  if a:append > 0
+    let val .= '%{airline#util#append('.func.')}'
+  elseif a:append < 0
+    return '%{airline#util#prepend('.func.')}'
+  else
+    return '%{'.func.'}'
+  endif
+  return val
+endfunction
+
+function! airline#section#create(parts)
+  return join(map(a:parts, 's:get_val(v:val, 0)'), '')
+endfunction
+
+function! airline#section#create_left(parts)
+  let _ = s:get_val(a:parts[0], 0)
+  for i in range(1, len(a:parts) - 1)
+    let _ .= s:get_val(a:parts[i], 1)
+  endfor
+  return _
+endfunction
+
+function! airline#section#create_right(parts)
+  let _ = ''
+  for i in range(0, len(a:parts) - 2)
+    let _ .= s:get_val(a:parts[i], -1)
+  endfor
+  let _ .= s:get_val(a:parts[-1], 0)
+  return _
+endfunction
+