Build without sudo requirements with default prefix

Make the standard "./configure && make && make install" work
as intended, that is, only require sudo permissions for
"make install", when the permissions of prefix's path require it.

Fixes #155

nullbios: fix asm macro for backup ram access

Commit ca710f9 added memory fencing hints for the compiler,
but in doing so, this broke the original asm instruction due
to how we did not guard symbol % when referencing %d0

Ref #132

Initial release tag