Minor documentation improvements.

git-svn-id: http://lufa-lib.googlecode.com/svn@2649 d5102386-fcda-11dd-9fdb-3debd5008f28
Make Mass Storage bootloader makefile variable naming consistent.

git-svn-id: http://lufa-lib.googlecode.com/svn@2650 d5102386-fcda-11dd-9fdb-3debd5008f28