Add support for custom reader

[SebastianSzturo]

Allows you to define a custom reader name for your property.

class Post
  property :new, default: false, accepts: [true, false], reader: :new?
end

post = Post.new(new: false)
post.new? # false

post[:new] = true
post.new? # true
post[:new] # true

[t6d]

Thanks a lot! 👍