Two schemes for Autocoder to produce relocatable decks

A new pseudo op RELOC with an index register tag such as X2 turns on
relocating output.

RELOC without an index register tag turns it off.

Load and SW instructions generated for loading have their addresses
tagged with the specified index register.  EX, XFR or END in a RELOC
region also get tagged.

Within a RELOC region, references to labels or relative references in
that RELOC region get modified by that index register on the next load
card using SBR in the 40-67 area if eight or fewer addresses are to be
relocated, or

....5...10...15...20...25...30...35...40...45...50...55...60...65...70.
HxxxyyyHxxxyyyHxxxyyyHxxxyyyHxxxyyy1001,008015,022029,036040HxxxyyyB001
HxxxyyyHxxxyyyHxxxyyyHxxxyyyHxxxyyyN001HxxxyyyHxxxyyy/061039,0010011001

if more than eight addresses are to be relocated (the greatest number
of addresses needing relocation on one card is 13, which can only occur
if they're all address constants, and at most seven of them have word
marks).  The /061039 is done earlier on the second card if fewer than
thirteen addresses need relocation.

ORG with an index tag would simply load the program without relocating
any of its addresses.  It would be the program's responsibility either
to relocate the addresses (probably using an overlay), or tag the
references with the appropriate index register.

The program is expected to initialize the specified index register
using the desired load address less the ORG at which the RELOC region is
assembled.  The assembler doesn't complain about load addresses in 1-80
if RELOC is on, so ORG at zero is OK.

The program is expected to set up its own linkage to the relocated code.