replace ehdr.e_wident[4] junk with standard e_ident[EI_NIDENT], add top-level Makefile, add TODO

TODO

@@ -0,0 +1,29 @@
+Elf36 Specification:
+
+- Do we want to adjust SHN_LORESERVE up to SHN_HIRESERVE, including SHN_XINDEX, to
+  account for the fact that we have 2 more bits available in Elf36_Half?
+  I'm inclined not to change, but to allow indices in [SHN_HIRESERVE+1,PDP10_UINT18_MAX]
+  as-is without going through SHN_XINDEX.
+
+- Same question for PN_XNUM?
+
+- Summarize the differences between Elf32 and Elf36 in a document somewhere.
+
+pdp10-stdio:
+
+- Handle non-seekable output files better (i.e., allow 8to9 to write to stdout)
+
+Tools:
+
+- size: implement it
+- strip: implement it
+- ld: implement it
+- readelf: add support for relocs
+- readelf: add support for program headers
+- as:
+  * add support for named sections
+  * add support for sub-sections
+  * add support for data directives (.word, .asciz, etc)
+  * add support for relocs
+  * add support for extended opcodes (emit second opcode after current .text section)
+  * add support for symbolic references to 30 or 36-bit addresses via something like %hi/%lo functions