#2 Convert tab to spaces.

[Hiroyuki Kurokawa]

Convert tab to 4(or 8, customizable) spaces. and
opposite.
Some people want this functionality.

+User can set converted space size on OptionDialog.
+User can select one convertion action from below on
OptionDialog.
1. no convertion.
2. convert tab to prefered number space.
3. convert space to tab.
+This convertion is made when to output the file.