Avirut Mehta

Replace environment variables in matchers as appropriate

2

I'd like to be able to use environment variables within my l4 matchers, e.g.: ```json "match": [ { "tls": { "sni": [ "{env.DOMAIN}" ] } }, { "http": [ {...

Hi, I'm unable to get any Python cells properly working (or at least as I believe they should) in Stencila. For example, I copied [some code](https://user-images.githubusercontent.com/1152336/43323662-462a1bdc-9180-11e8-9862-b7d6da0c3070.png) from [another issue](https://github.com/stencila/py/issues/20) written...