Add known-issues documentation section to the various LUFA bootloaders.

git-svn-id: http://lufa-lib.googlecode.com/svn/trunk@2657 d5102386-fcda-11dd-9fdb-3debd5008f28
Fixed Low Speed USB devices broken when using the library HID Class driver (thanks to Michael).

git-svn-id: http://lufa-lib.googlecode.com/svn/trunk@2658 d5102386-fcda-11dd-9fdb-3debd5008f28
Fix incorrect Interrupt disable function for the XMEGA architecture (thanks to Simon Küppers).

git-svn-id: http://lufa-lib.googlecode.com/svn/trunk@2659 d5102386-fcda-11dd-9fdb-3debd5008f28