Add a styleguide

[devromik]

We should create an automatic formatter for IDEA.
The list of rules:

1. There should be an empty line after a class header:

public abstract class A {
    
      public final MetricName name;
      ...
}

There should be no empty lines if the definition of the class consists only of constants.

public abstract class A {
      public static final MetricName DEFAULT_NAME_PREFIX = MetricName.of("Buffers");
}

2. We use only 4-space indentation for all the cases.
3. We use the following formatting schema for long enough parameter lists (2+ usually but it depends):

protected Supplier<LongVarConfigBuilder> longVarConfigBuilderSupplier(
        String description, 
        MetricDimension... dimensions) {

        ...
}

or

protected Supplier<LongVarConfigBuilder> longVarConfigBuilderSupplier(
        String description, MetricDimension... dimensions) {

        ...
}

We add an empty line after a multi-line definition. For example,

registry.longVar(
    nameWithSuffix("startTime"),
    runtimeMxBean::getStartTime,
    longVarConfigBuilderSupplier("The start time of the Java virtual machine in milliseconds"));

registry.longVar(
     nameWithSuffix("uptime", "ms"),
     runtimeMxBean::getUptime,
     longVarConfigBuilderSupplier("The uptime of the Java virtual machine in milliseconds"));

5. We don't use the prefix 'is' for fields or parameters, only for methods: isDimensional.
6. We don't add an empty line after a method signature:

public void produceMetrics(MetricRegistry registry) {
   // no empty line here
    for (int i = 0; i < ATTRS.length; ++i) { 

7. We don't use a space for type casting: (double)i
8. There should be an empty line before and after if/try inside a method body (but not for the last statement).
9. There should be no empty before closing brace in a class definition.