Adding reference to Skip Lists paper.
Move the PoolHasRange test to pool.c so that all frees (including internal ones) get the check.
Converting MPS procedure documentation to reStructuredText.
Fixing up reStructuredText syntax.
Improve the discussion of testing dependencies for staleness.
Improvements to clarity of weak hash table implementation:
* TAG_SIZE was changed to TAG_COUNT in the code, so make the corresponding change in the manual.
* Avoid the "+= 2" hack: use TAG_COUNT(UNTAG_COUNT(...) + 1). Clarity is more important than speed here.
* Use obj_unused for unused hash table entries so that there can be no confusion between NULL meaning "unused" and NULL meaning "splatted by the garbage collector".
* Add references from the example code to the notes.
Fix typo.
Fix typo.
Add #memorypoolsystem to contact page and to sidebar.
Document the intention behind mps_ld_isstale rather than the implementation: it captures the intention of testing whether a particular dependency is stale (even though the implementation in fact tests whether any dependency is stale). Add new function mps_ls_isstale_any for expressing the intention of testing whether any dependencey is stale. The two functions have  the same implementation at present, but the separation gives us the freedom to return a more precise result from mps_ld_isstale in future.
Forgot to document thread-safety property of mps_ld_isstale_any.
No need to compile arg.c separately: included in mps.c since change 181994.