Believed prototype of setPercentages functionality

Believe I have a working function for setting the percentages of a Post
Object after it is saved, however I am yet to actually test it
Fixed parentheses typo
Changed afterSave to beforeSave - only way it wold work
Made it impossible for a percentage value to be null - it would be 0 instead
Null check didn't work - changed to isNaN(percentage)
Merge pull request #1 from dcgoss/setPercentages

Merged setPercentages branch to master