Linter: add "hard-coded constant" warning

Tracking issue: #501 

We would like to warn code like:

```python
print! 3.141592653589793 # use math.pi
print! 2.718281828459045 # use math.e
```

Constants that can be referenced should be displayed as hints instead of hard-coded values.

(It would be nice to be able to warn about values that match constants that exist in the standard library in addition to numerical values.)
