Add `jekyll-image-tag` plugin for jekyll-friendly image inserts

- Add `jekyll-image-tag` for jekyll-friendly insertion of images in
markdown post
- -Add `jekyll-image-tag plugin` in `_plugins` folder
- - Add `post-inline-2` preset for side-by-side images in posts in
`_config.yml`
- - Add css class to set `display:inline` for multiple images per row in
`css/post.css`
- Minor spell-checks