Send Accept-Encoding header

The Accept-Encoding header should be set to `Accept-Encoding: identity` when requesting a h-card or h-entry for cases where a server or proxy sends compressed data in the absence of said header.

Start by locating the code path that requests h-card or h-entry data and inspect how request headers are constructed. The work is done when those requests send `Accept-Encoding: identity` and the behavior is covered by an appropriate test, though the issue does not name a file or test.

Written by the indexing model from the issue text.