added stavesPerPage computation for viewport relations (found that a relation below width/height=1.55 should create 3 staves per page, less should create 2); added filename extraction (foo.staves -> foo.pdf)
added stavesPerPage computation for viewport relations (found that a relation below width/height=1.55 should create 3 staves per page, less should create 2); added filename extraction (foo.staves -> foo.pdf)

dominikschreiber/staves