Merge pull request #20 from sacjaya/Siddhi-3.0.0

removing validation classes
refining exception hierarchy
adding support for functions
adding support for aggregated attributes
renaming varaibels of MetaStreamEvent
adding extension loader
Merge pull request #21 from sacjaya/Siddhi-3.0.0

Changes based on code review
Extension support
Length window implementation
Merge branch 'Siddhi-3.0.0' of https://github.com/wso2-dev/siddhi into Siddhi-3.0.0