Bind 'gnus-inhibit-mime-unbuttonizing' in 'autocrypt-gnus--get-part'

This prevents Gnus from inserting additional buttons when calling
Use a custom constructor for 'autocrypt-peer'
Bump version to 0.4.1 for GNU ELPA
Assign copyright to the FSF
Relicense autocrypt under GPL-3
Recommend GNU ELPA as installation archive
Add auto-generated package.el files to .gitignore
Add a 'get-part' implementation for Gnus
Fold 'defalias' definitions for the MUA generic functions
Avoid usage of 'defsubst' where unnecessary
Remove setup example from the README
Add missing `-hook` suffix in readme hook name
Run M-x repunctuate-sentences on README
Remember to remove hook as modified in dd400cb
Prefer mu4e-view-rendered-hook if bound

Thanks to Thierry Volpiatto for notifying me to this change:
Adjust header formatting

Specifically the titles are now capitalised instead of uncased, and
the outline-minor-mode indentation is raised to 4 (one more than the
"Code" section).
Inline autocrypt-find-function
Fix custom type of autocrypt-process-header
Further improve robustness of autocrypt-process-header
Install process-header into gnus-select-article-hook