fix wrong ".." ellipsis and replace "..." by proper ellipsis '…'

**/!\** There is still an issue in this page, the John Gruber quote isn't processed as a quotation by the Jekyll Markdown engine… I can't figure out why.

> Markdown is a text-to-HTML conversion tool for web writers. Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML).

![whatismarkdown_quote_error](https://cloud.githubusercontent.com/assets/362710/3051632/b2b0288c-e18f-11e3-873e-8bb471772fc3.png)