Fixes 65851406_about_hashes_master

* Learned to create hashes in curly brackets {}
* Learned that hash size is equal to the number of key => value pairs
* Learned that you can access hash values by specifying the key, but it's better to use hash.fetch because it
  will raise an error if that key doesn't exist (versus just returning nil)
* To change a hash value, all you have to do is specify a new value for the key
* I learned that hashes are unordered and that they can be equal even if the key => pairs are not in the same
  order
* Hash keys and hash values are both in separate arrays and you can use .include? in either to see if a certain 
  value is present
* Hashes can be combined with .merge
* Default values for keys can be specified and will have the same object_id for all keys
* You can use a block to specify the default value of Hash keys

[#65851406]