Ignore newlines per md standard.
Add to changelog changes for markdown.
 Merge branch 'new_lines_markdown' into 'master'

New Lines Behaviour in Markdown

Per markdown specification, only render line-breaks when you end a line with two or more spaces.
Clear rake task only if defined

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'master' of dev.gitlab.org:gitlab/gitlabhq