Add with-extra-context macro

[DeLaGuardo]

This macro is usefull when you don't know full context at logging time.

E.g. for more detailed logging during evaluation some logical steps:

(let [session (get-random-session)]
  (with-context {:session "some random session"}
    (log "Catch request")
    (let [user (get-user-data)]
      (with-extra-context {:user user}
        (info "log user data with session as a scope")))))

[ptaoussanis]

Hi Kirill, thanks for this! Hope you're well!

To be honest I'm not too keen on adding another macro just for this. It's already pretty easy for someone to do (with-context (merge *context* {}) ...).

Appreciate the PR though, thanks!

[b-ryan]

Just wanted to throw in my 2c, which is that I expected with-context to work this way and spent a bit searching the docs for this functionality. Perhaps an acceptable alternative would be to provide your suggestion when searching the readme or the docs for with-context. Overall it didn't take too long to arrive here though.

[b-ryan]

To clarify: when I said "Perhaps an acceptable alternative..." I mean acceptable from your point of view, not mine :D