Feature Request: Built in breakpoint

[Daniel Olshansky]

This is a followup for this github PR. Please note that I'm very interested in implementing this feature myself, but was hoping for some feedback from the community before I invest time in it.

I recently read this article about breakpoints in python 3, which implemented PEP553, and a few things stood out:

1. A breakpoint function is built-in, not requiring imports (i.e. requires). I realize adding a require is not hard, but having breakpoint become a function that's accessible everywhere will really reduce the friction for its usage.
2. Breakpoints can be enabled/disabled via an environment variable. This can be the default in production to avoid unnecessary requires.
3. The type of debugger can be modified via the environment variable as well. This is probably not necessary for the first iteration of this.

I was wondering what people's opinions are about points 1 & 2, and eventually point 3 as well.

[OvermindDL1]

I'm curious about `3`, what do you mean type of debugger?  Is it going to be pluggable?  Like via over IEX, or perhaps over a remote socket, or a hosted SSH connection, etc...?