Return all namespaces created in a file instead of the first one

[TimoFreiberg]

Creating multiple namespaces in one file is unidiomatic, but I'd like to support it properly anyway.

Naively reading the entire file and returning all ns and in-ns forms is a bad idea because reading namespace aliased keywords without having evaluated the namespace aliases will crash (see the bug described here: #3).

The current plan is to build on the good work from the kibit project and use https://github.com/TimoFreiberg/total-reader to read the entire file.