Add block-style hash 'Blash'

Just an idea I was kicking around for a blocky style to creating sub-hashes, similar(if you squint) to `Somethingfile`-style configuration dsls.

Also considered including the ability for the method calls that take the block to also take a single argument, which would craft another level of sub hash, like so

```
b = Blash.new

b.test :one do |one|
  one.foo = "bar"
end
b.test :two do |two|
  two.hurp = "derp"
end

b.test.one.foo # => "bar"
b.test.two.hurp # => "derp"
```