Megapack

I'll propose all this stuff at once, **but I'm ready to split into different PRs** if you want just a subset.

- Add support for Rational/Complex Literal (Ruby 2.1), e.g. `23i` and `23r`
- Add Symbols (Intern) percent string support, e.g. `%i[some symbols]` and  `%I[some #{:symbols}]`
- Add <kbd>i⇥</kbd> to insert `inspect`
- Add @ expantion to memoized ivar (see below)
- Skip multiple extensions in the class name, e.g. the class name generated from a file named `my_class.js.rb` will be `MyClass` instead of `MyClass.js`


---

### Add @ expantion to memoized ivar

Will expand `@` to a memoized assignment of a variable with the same name as the including method.

#### General case

```ruby
def some_method
  @⇥
end
```
is expanded to:
```ruby
def some_method
  @some_method ||= some_method
end
```

#### With previous content

```ruby
def some_method
  @⇥previous_content
end
```
is expanded to:

```ruby
def some_method
  @some_method ||= previous_content
end
```

#### Inside `initialize`

```ruby
def initialize
  @⇥
end
```
is expanded to:

```ruby
def initialize
  @instance_variable = instance_variable
end
```