Separate template filters and functions into its own module

First, this is nice project.
I just fork it and want to jump right away to give some contribution.

I don't know if it is necessary or not, but what I have done is to separate all functions that related to template functions and filters to its own module to anticipate more-and-more addition of filters and functions. the test for this also have been updated.

so, in the future all template related functions and filters will be in one place.
thank you, your feedback are appreciated.