Update plugins.html.md

added links to Alias and Shortcodes plugins.
Added link to scheduling plugin on plugins page.
Update contribute.html.md

Made the instructions a bit more clear in regards to plugin development
Update contribute.html.md

Improved some development and pull request instructions
Update contribute.html.md

Redid the pull request, publishing, and test docpad against plugins sections
Update contribute.html.md

Added link to documentation pull request criteria
Update CONTRIBUTING.md

Added mention of GFM to criteria
Merge pull request #41 from field/patch-4

Update plugins.html.md
Merged in #42
added coffeemugg plugin links
Merge pull request #73 from pflannery/patch-1

added coffeemugg plugin links
Updated contributing guide for latest docpad-extras changes
Updated for ./app executable on docpad-extras repo
Fixed plugin URL for js2coffee plugin

There is no docpad/docpad-plugin-js2coffee repo and I couldn't find a
valid repo so I just pointed it to the NPM package page.
Fixed duplicate plugins

There were two version for the `dateurls` plugin so I removed the NPM
package version and left the GitHub version.

I also fixed the order of the `datefromfilename` plugin, it wasn't in
the Ds, it was in the Cs.
Re-worded some stuff on troubleshooting section

I also fixed a typo and added a note on the FAQ section about document
files and text files.
Changed some wording on the troubleshooting docs
Changed some wording on the troubleshooting docs
Clarified stance on binary formats in FAQ
Fix license year in README