reader macros for hidden packages

[jgart]

Hi Guixers,

Out of curiosity, is it possible to make reader macros like this with guile?

```
@hidden
(define-public python-httplib2
  (package
    (name "python-httplib2")
    (version "0.9.2")
    (source
     (origin
       (method url-fetch)
       (uri (pypi-uri "httplib2" version))
       (sha256
        (base32
         "126rsryvw9vhbf3qmsfw9lf4l4xm2srmgs439lgma4cpag4s3ay3"))))
    (build-system python-build-system)
    (home-page "https://github.com/jcgregorio/httplib2";)
    (synopsis "Comprehensive HTTP client library")
    (description
     "A comprehensive HTTP client library supporting many features left out of
other HTTP libraries.")
    (license license:expat)))
```

The above would make the package hidden by using `hidden-package`.

I would imagine so... I'm just not sure where to begin looking to achieve 
something like that syntax.

See more discussion here:

https://todo.sr.ht/~whereiseveryone/guixrus/356

all best,

jgart