Documentation

The documentation for this project is needs some work. Here are some areas to work on:

* [hop:addChainedTask](http://dart-lang.github.io/hop/#hop/hop@id_addChainedTask)
* [hop:Task](http://dart-lang.github.io/hop/#hop/hop.Task)
* [hop:TaskArgument](http://dart-lang.github.io/hop/#hop/hop.TaskArgument)
* [hop_tasks:branchForDir](http://dart-lang.github.io/hop/#hop/hop_tasks@id_branchForDir)
* [hop_tasks:createBenchTask](http://dart-lang.github.io/hop/#hop/hop_tasks@id_createBenchTask)
* [hop_tasks:createProcessTask](http://dart-lang.github.io/hop/#hop/hop_tasks@id_createProcessTask)
* etc...

Also documentation has some formatting issues.