Added tny_mime_part_get_header_pairs

[Philip Van Hoof <spam pvanhoof be>]

I added the TnyPair type and the tny_mime_part_get_header_pairs API.

This API makes it possible to get any header once the message is
received (not just the ones in TnyHeader). It's indeed on the
TnyMimePart type because each individual mime part can have its own
headers. The entire message, being an inherited specialised mime part,
is just like any other mime part (it contains zero or more headers).

The tny_mime_part_get_header_pairs interface is obviously implemented in
libtinymail-camel.

You use it like any other list method: give a TnyList instance, that
instance will become the owner of the TnyPair instances. A TnyPair
instance will freeup its name and value properties upon finalisation.

The documentation, like API reference documentation, is also updated.

-- 
Philip Van Hoof, software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://www.pvanhoof.be/blog