Fluent setter (#9)

* Moved functions

* Added setter functions

* added test and edited travis

* updated readme

Can set start day (#7)

* started using firstdayofweek

* removed redundant variable

fixed bug in difference as float and readme update (#6)

gomodule support (#5)

gomodule support (#5)

Code update (#3)

* changed use of constant in godate

* changed use of constants in test

Updated Readme