SimpleExprWithBraceChecker

#### About this checker

This checker detects the brace contains a simple expression.

[Effective Scala](http://twitter.github.io/effectivescala/#Formatting-Braces) suggests "Braces are used to create compound expressions, where the value of the compound expression is the last expression in the list. Avoid using braces for simple expressions".

We define `a simple expression` as a single expression.

For example,
the checker allows
    
    def foo(x: Int) = x * 2

but, does not allow

    def foo(x: Int) = {
      x * 2
    }

#### How to configure
By default configuration, the checker detects nothing.
To use this rule, you need to specify the target tokens by using "TargetToken" parameter in a config file.
Available tokens are "def,val,var,if,for,while,do,case"

Here is an example configuration,

    <checker class="org.scalastyle.scalariform.SimpleExprWithBraceChecker">
        <parameters>
            <parameter name="targetToken">if, def, val, var</parameter>
        </parameter>
    <checker>