Adding new files to the gitignore

The gitignore file tells git which files it should not track from now
on. This commit says that it should not track my sublime text project
files.
Updating the site configuration

The configuration changes in _config.yml are now used as variables throughout
the blog. In general, it's bad practice to use raw text as opposed to variables.
Merge pull request #1 from pspeter3/master

Adding some more structure to your project