Made the time/index/year _from_path methods public

We need these methods in the next step
Moved CatLastCommand -> LimitLastCommand
Changed command implementation: Build up a Tree instance in here, please
We must include these modules in here
Merge branch 'move-last_command_to_limit_command'
Merge branch 'refactor'
Fixed stupid typo
Merge branch 'fix-labels'
Added Entry#add_category
Implemented CategorizeCommand class implementation
Ensure the category is written
Merge branch 'implement-categorize_command'
Added Rakefile with test task
Added .travis.yml file
Merge pull request #61 from matthiasbeyer/add-travis

Add travis
Added travis image to readme
Merge branch 'add-travis-image'
Fixed implementation for parse_{start,end}_date
Do not return 1 in case the variable is nil, we must handle this outside
Rewrote #search_in? Implementation