Move files to a new build system, step 1: directory structure.

(this is not meant to currently be pretty, and maybe not even work)
cleanup moved files
build fixes
move man pages to doc
Get rid of old directory structure.
add top-level Makefile
Use <bsd/vis.h> on Linux instead of <vis.h>
(does this apply universally?)
set default opt/dbg to -g for now
Enable NFS
rename doc to man
Merge branch 'buildreorg' of github.com:stacktic/fs-utils into buildreorg
Added fsu_mount3 to specify readonly/readwrite mount mode
Removed fsu_mount3, only keep fsu_mount with 3 arguments
match instructions with current status
Simplify usage (thanks to stacktic) and note installation caveat.

(there is no "make install")