Make projects a separate collection

[dmsnell]

Attempts to finally resolve #20

Previously, the projects were defined inside of a data collection in projects.yml in a tight format. I found this difficult to work with because of the way the content squashed together and how leaving a single line for the project description made it feel more like a plain text string instead of a rich markup field.

Now, projects become their own collection found under the _projects/ folder, one file per project. Each project has front-matter specifying data related to the project, and the description has been moved below the front matter into the Markdown area and accessible as content.

Moving from a list of items into a folder of pages broke the inherent sort order of the list, so I have updated index.html and projects.html correspondingly to enforce a new sort based on the date given for each project. I pulled the dates from the git history on the project.yml file.

To illustrate the new flexibility I have updated a couple of the descriptions for the City SDK project and the National Day of Civic Hacking project with some markup such as links, bold, and italic formatting.

Additionally I have removed the Tucson Answers project because I could not find any reference to Tucson Answers with that search query on Google other than this site, but the GitHub repository for it is basically empty. Not really a flagship project, but we can pull it back if we want.

P.S. Please pardon the udpate in the branch name. My bad.

cc: @meiqimichelle