`bind-last` meta command

[arthurpaulino]

[Post #968]
The bind-last meta command binds the result of the last computation to a symbol:

user> 42
[1 iteration] => 42
user> !(bind-last foo)
user> foo
[1 iteration] => 42

Once it's implemented, we should change def-load-data to just load-data, which doesn't bind anything. Then binding can be done manually with bind-last.