Write a simple way of adding a before filter onto a given method of a class.

Here is some Psudo code for you as an example of the functionalty I'm looking for.

```
a = new AClass

a.talk()
# Logs:
#   "Hello"

a.before('talk', func { log('I'm First!')  })

a.talk()
# Logs:
#   "I'm First!"
#   "Hello"
```