Support divelogs.de exports that include Cyrillic characters

divelogs.de sends us XML files that explicitly state that they are in
ISO-8859-1 encoding (which is true). These files contain the HTML encoded
Cyrillic characters. Once we decode those characters the resulting file is
actually UTF-8 encoded (which is a superset of ISO-8859-1). That seriously
confuses libxml when it tries to parse things.

So instead recognize divelogs.de files and skip the encoding declaration
for them before decoding the HTML encoded non-ISO-8859-1 characters.

This does show, however, that divelogs.de incorrectly truncates the
encoded strings (at least in some sample data that I created the parsing
throws errors because of that).

Reported-by: Sergey Starosek <sergey.starosek@gmail.com>
Based-on-code-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Use a generic 64bit int type

The zip_int64_t type appears to be missing with mingw so it breaks my cross
builds - and this is clearly equivalent.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>