re-organize the tests and corresponding modules

Reorganize following modules
  * utils.DateRelated
  * utils.Composition
Recreate the StockDaily class from DataFrame

Extends the StockDaily from DataFrame.
Override the __getitem__ method to create useful columes when they are
retrieved.
Add Worker and Model class

Worker is suppose to be a calculator on a single thread.
Model is the definition of a stock trend guess.

Add document for numpy.