Update dub.json with more actual information.
Add a little better formatting to StdoutTodoFileWriter.
Refactor all task related objects. Add initial support for lua based addon system.

Tasks are now a struct called Task.  TodoTask class now processes lines and returns a tuple(Task, bool) that contains a Task and a boolean value that signifies if it is a valid task.
Add an alias ReturnValues for return values in TodoTask and TodoFileReader.

This makes the code a little more readable.
Move task object creation to a position before if check thus removing an extra object.
Add luaaddon.d which will be used for exporting todos to various formats. Update app.d accordingly
Remove apitest.lua.
Remove todofilewriter.d. Using lua now for exporting todo lists.
Move stdout.lua to stdout directory. Each addon will have its own directory now.
Add csv, html, json, markdown barebones addons. Update stdout addon use Stdout in its leading output.