Refractored trig constructor to C++11 standards.

Following Ondrej's advice this PR improves the constructor
from #168 to C++11 standards
Removed getter and setter from TrigFunction

Also removed extra whitespace.
Added `get_arg`, travis build fails without it
Merge pull request #170 from sushant-hiray/refractor

Refactored the constructors for Trignometric classes