Source code for vibe.d listenTCP()

[Chris Piker]

Hi D

I'm trying out the vibe.d framework for the first time and it 
looks like many of the functions mutate some hidden global state. 
  Take for example `listenTCP`.  To help me build a mental 
picuture of the framework I'd like to see what global state is 
mutated, but for the life of me I can't even find the source code 
to listenTCP().  The obvious method of:
```bash
git clone git at github.com:vibe-d/vibe.d.git
cd vibe.d
grep -R -n listenTCP
```
returns many instances where listenTCP is used, but none that 
look like a definition.  It's quite possible I just overlooked 
it, or maybe it's implemented as a mixin or something weird like 
that.

Anyway if someone can just help me find the source code to 
listenTCP inside vibe.d I'd be grateful.

Thanks for your time,