Ability to search Github repositories  for templates

I have added a new command to allow users to search Github for templates. For example:
```
g8 search android-sbt

gseitz/android-sbt-project.g8
	 A g8 template project for android development
sdb/android-sbt-quick.g8
	 giter8 template for a basic sbt project for your Android apps
bcart3r/droid.g8
	 base android sbt template
xuwei-k/android.g8
	 Android sbt project giter8 template
nrf110/android-app.g8
	 giter8 template for generating android projects with scala and sbt
```

I haven't found a way to make the option parsing support search terms with spaces. Thus if you want spaces you will have to do something like this:
```
g8 search "scala js"

sebnozzi/scala-js.g8
	 Giter8 Template for Scala.js Projects
dkrieg/scalatra-angularjs-seed.g8
	 This project is a g8 template for a Scalatra + AngularJS web app.
```