print values without using "echo"
Coming from Python, I really like that you can do this:

```python
>>> a = 7
>>> a
7
>>> 1+1
2
```

That is, when you create a variable, you can print its value without using the `print()` function. The same is true for expressions.

INim works like this at the moment:

```nim
nim> var a = 7
nim> a
Error: expression 'a' is of type 'int' and has to be discarded; start of expression here: inim_1539330313.nim(1, 0)
nim> 1+1
Error: expression '2' is of type 'int literal(2)' and has to be discarded; start of expression here: inim_1539330313.nim(1, 0)
nim>
```

It would be great if we could mimic the Python REPL. Maybe it could be done like this: try to execute the line as it is. If there is an error, rewrite the line by adding "echo" to the beginning of the line and re-execute the line. The second time output everything.

Or, a less appealing solution could be to define an alias function called "e" for instance that points on "echo". Thus we could print easier:

```nim
>>> var a = 7
>>> e a    # short for `echo a`
7
>>>