Dispose of m and post directories

I never managed to be so precise because it took to much time
per student to evaluate at this level of detail.
subr_http.py: retrieve(): remove noisy parameter

Of course I checked that no invocation of retrieve() in the tree
was using the noisy parameter.
Always use subr_http.retrieve()

To this end, also extend subr_http.retrieve() API for the
caller to get the headers, if needed.
subr_http.py: refactor retrieve()
subr_misc.py: maintenance

Remove unneeded function and repair out-of-date docstring.
subr_bit.ly: maintenance

Improve and/or correct docstrings and comments. Also, remove
the unused named parameter called 'noisy'.
Move readfile() functionality from subr_bitly to subr_misc
subr_bitly.py: add main() function
subr_rss.fetch(): remove unused noisy parameter
Don't return a tuple in subr_rss.fetch()
Rename rss_fetch.py to main_rss.py

The idea is that, if a file is named main_rss.py, one that wants
to learn how the code is structured understands that such file is
a good starting point.
Refector main_rss.py

While refactoring, also make the code of subr_rss.py
more precise as well.
subr_http.py: tweak the handling of headers

- Also print "[snip]" to communicate the operator that we only
  print some of the request headers;

- No need to convert headers name to lowercase: apparently this
  is already done by httplib.
Merge branch 'master' of github.com:bassosimone/rivoluzionedigitale