https://github.com/o2platform/FluentSharp/issues/17

Fix for https://github.com/o2platform/FluentSharp/issues/17
Added extra validation for trim function
refactored issue with trim , lower and upper functions
Merge pull request #38 from alexandrustanimir/master

Fixed lower,upper and trim functions. (https://github.com/o2platform/FluentSharp/issues/17)