add object *s4m* to hold patcher attributes for access from Scheme

[iainctduncan]

make it work like s7, and allow getting attributes:
ins
outs
heap-size
file
thread

[iainctduncan]

added hashtable for attributes, s4m, with attributes set in C for :ins and :outs
added public wrapper, s4m for read only access:
(s4m :ins) (s4m :outs)