Change filenames of markdown files

[Madusudanan]

Error reading file ..... Document '_setup/001-install.md' does not have a valid date in the YAML front matter.

Instead of having 001-install.md we can have it as 2015-11-19-install.md.

• We can eliminate the nasty issues popping in jekyll console.
• We can have the last updated date listed in the page itself, might be helpful for users.

This also opens up many possibilities, but I don't feel having 001 in the file name helpful in any way.

I can send a pull request if I know the dates of the published articles.