Rule: no-plusplus

Created the no-plusplus rule. This rule disallows the use of unary operators, `++` and `--`, as such the following would be flagged:

```js
var foo = 42;
foo++;
foo--;
```

This rule matches JSHint's **plusplus** rule.
Better documentation for the `no-plusplus` rule.
Merge pull request #126 from iancmyers/rule-no-plusplus

Rule: no-plusplus