Set baseurl liquid variable to allow for easier local jekyll testing

Signed-off-by: Jordan Justen <jljusten@gmail.com>
Make links absolute to allow sub-directories

Signed-off-by: Jordan Justen <jljusten@gmail.com>
Move edk2.html page to edk2/

Signed-off-by: Jordan Justen <jljusten@gmail.com>