Update _post.scss

Evened padding on top and bottom of post, included declaration to remove `margin-bottom` from the last `.highlight` in the post.
Update _header.scss

Header `padding-bottom` now matches `padding-top` of post.
Update _post.scss

Comment on line 14 - something to consider.
Update _post.scss

Set declaration to remove `margin-bottom` from last `p` in `.post`.
Merge pull request #1 from AdamWhitcroft/gh-pages

Minor tweaks