Fix improper header separator for X-OfflineIMAP header

For servers without UIDPLUS we are inserting additional header
just after transformation '\n' -> CRLF was done.  addmessageheaders()
was written to work with just '\n' as the separator, so X-OfflineIMAP
header wasn't preceeded by the CRLF, but just by '\n'.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Add version qualifier to differentiate releases and development ones

It is always good to see which version we're talking about, so I had
added explicit marker for -devel, -release, -rcX and other states of
the OfflineIMAP.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
More clearly show results of folder name translation

For cases like
  http://article.gmane.org/gmane.mail.imap.offlineimap.general/6468
it is beneficial to see that folder name was translated and the result
of this translation on a single line: having log like
{{{
Folder Boring/Wreck [acc: tmarble@info9.net]:
 Syncing Boring/Breck: Gmail -> Maildir
}}}
with translated name on the "Folder" line and original one on the
"Syncing" line isn't very intuitive.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Merge pull request #67 from danmilon/fix-docs-folderfilter-typo

docs: fix folderfilter typo
Fix Markdown formatting

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
Rename addmessageheader()'s crlf parameter to linebreak

The parameter's value is a string representing the linebreak,
and can sometimes contain just '\n', in which case naming it
crlf is slightly misleading.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
addmessageheader: fix case #2 and flesh out docstring

The example illustrations were slightly cryptic;
modify them to be more obvious.

Fix case #2 (message starts with two line breaks)
where additional line break was shown and coded.

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
addmessageheader(): add debug for header insertion

Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>