Register usage of GETLINE$() function

D0 Trap function code, return value (Traps, returning to S*BASIC, ...)
D1 Size.l of buffer (BV.CHRIX destroys d0-d3!), no.w of bytes fetched, stringlen.w
D2 Size of buffer (currently constant STRMAX-6)
D3 Timeout for IO-Traps
D4 0.w: trailing LF must be stripped, else do not strip LF,
        temporary copy of a5 for testing if a5 is on longword boundary
D5 size of buffer to reserve on math stack (S*BASIC stack/RI-stack)
D6 no.w of bytes fetched, stringlen.w, no.w of bytes remaining, no.w of
   longwords to copy
D7 1.l if CON chan. else 0 (from getChan), 0 if no remaining word must be copied

A0 channel id (from getChan)
A1 BV.RIP (destroyed by IO.PEND)
A2
A3 Pointer to first parameter (updated by getchan). Currently getchan returns
   with Bad parameter if more than one parameter is passed to GETLINE$()
A4 BV.RIP, decremented while copying and will be copied back to A1 before return
A5 Pointer to last parameter, base of buffer for IO.FLINE, pointer after word
   holding last word of fetched string, will be decremented while copying
A6 MUST NOT BE WRITTEN TO IN S*BASIC EXTENSIONS!
A7 Stack pointer used and restored by getChan
