load-data-readers! in pods

An https://github.com/levand/immuconf user asked in Slack how he can access config variables during compilation. A macro would usually do the trick but in this case the pod compiling the ClojureScript sources and running the macro does not have the reader function for the immuconf specific tags.

If I understand the issue correctly I see the following options

- We set `*data-readers*` in pods after initialization
- We move `boot.core/load-data-readers!` into a namespace that is available in pods and advise users to call it if they need support for dependency-imported reader tags.

**I didn't reproduce this issue so maybe it's absolute bogus.
The initial report it seemed plausible though.**