add rule that checks for assignments in while/if/.. clauses

[mozfreddyb]

It's a common mistake to write = instead of ==. We would most likely check for node types of AssignmentExpressions in nodes of type

• ConditionalExpression (this is the ternary thing)
• SwitchStatement
• IfStatement
• WhileStatement
• ForStatement, ForInStatement, ForOfStatement,

Thanks to @joernchen for suggesting this :P

[codelion]

I sent in a pull request for review which adds this feature. Do let me know if you need me to make any modifications.