Add config for whitespace inside array-notation MemberExpression.

Adds whiteSpace.before.MemberExpressionClosing and
whiteSpace.after.MemberExpressionOpening to expression liks `obj[prop]`.
Regular dot-notation (`obj.prop`) is unchanged.
Merge pull request #67 from jzaefferer/member-expression-ws

Add config for whitespace inside array-notation MemberExpression.