Wins losses on player

[straydogstudio]

What this does:

• Adds wins / losses to the player model
• Adds one convenience method for percentage of wins

Discussion items:

• The user should not be able to update their wins or losses. How should this be implemented and tested in Pundit?
• Where in the model would this value be set?
• Documentation not taken care of. What should be done for these kind of fields that are not parameters but are available on read.