Add rules for formatting attributes

[terrajobst]

This adds two additional rules for dealing with attributes:

Removing superfluous parentheses

It's conventional to omit parentheses when the attribute doesn't take any arguments, for example:

[target: SomeAtt()]

becomes

[target: SomeAtt]

Separating attribute lists

Most folks only use a single attribute in an attribute list, although the syntax supports multiple attributes. In most cases, putting attributes in separate lists is beneficial because it improves readability and allows better diffs.

This changes code like this:

[Serializable, Category("Catagory"), DefaultValue(1)]

to

[Serializable]
[Category("Catagory")]
[DefaultValue(1)]

The only exception are attributes for parameters. In interop code, it's quite common to mark parameters with [In] and [Out]. Since the attributes are usually written inline, i.e. not on separate lines, it's actually beneficial to no split them into separate lists.

This means that code like this is left as-is:

void NativeFun([In, Out] int* target)

[terrajobst]

@jaredpar

[jaredpar]

👍

Gave some feedback on a couple of small issues to consider.

[terrajobst]

Sorry, but I can't change the code anymore as I have the perfect number of lines being added! :-)

Just kidding, I'll take a look.