change URL for "Contents" option in "Help" menu

I propose that the address for the help contents is changed to docs.hexchat.org over simply being hexchat.org.
Merge pull request #398 from thor/patch-1

change URL for "Contents" option in "Help" menu
fix tray menu placement issues

notably top taskbar issues on windows
Add autojoin back
Make sure we don't auto-load HexTray
Fix bug in url.c at re_host().

Unlike the other re_foo() functions it was not checking immediately
and returning if host_ret had already been filled in.  This would
causes a memory leak since the previous GRegex would be lost.
Merge pull request #407 from RichardHitt/master

Fix bug in url.c at re_host().