Typos and other formatting changes

- Read through the complete Contributing wiki article and noticed that there were a couple things that weren't correct, so added them all to this commit.
- As per the instructions, added blank line before HTML markup.
- Noticed that the heading for blockquotes seemed to be getting indented due to the previous formatting, so added additional line, plus ensured that remaining headings were consistent.
Merge pull request #15 from gep13/typos

Typos and other formatting changes