add Previm and window management

sources_non_forked/previm/autoload/vital.vim

@@ -0,0 +1,12 @@
+function! vital#of(name)
+  let files = globpath(&runtimepath, 'autoload/vital/' . a:name . '.vital')
+  let file = split(files, "\n")
+  if empty(file)
+    throw 'vital: version file not found: ' . a:name
+  endif
+  let ver = readfile(file[0], 'b')
+  if empty(ver)
+    throw 'vital: invalid version file: ' . a:name
+  endif
+  return vital#_{substitute(ver[0], '\W', '', 'g')}#new()
+endfunction