Fix vimrc, and add plugin's patch file

If you execute `ctags -R`, `./tags` is created.
And then, be able to execute tag jump by reading the file.

Disabled setting of markdown folding
Don't like default indent setting,
so add variables for changeable indent setting.
If you want to activate this variables,
have to apply patch in `patches/vim-markdown/indent.patch`.
Please read `patch/vim-markdown/README`.