(put ds key value)
Associate a key with a value in any mutable associative data
structure. Indexed data structures (arrays and buffers) only accept
non-negative integer keys, and will expand if an out of bounds value is
provided. In an array, extra space will be filled with nils, and in a
buffer, extra space will be filled with 0 bytes. In a table, putting a
key that is contained in the table prototype will hide the association
defined by the prototype, but will not mutate the prototype table.
Putting a value nil into a table will remove the key from the table.
Returns the data structure ds.