http.server: handle certain parse-errors from the peg vocab

Browsers that can't verify the certificate doesn't send any request at
all which causes parse-errors to be unnecessarily thrown and logged.
peg: add 'got' slot to parse-error, so you get a little more info about why the parsing fails
peg.debugger: don't use formatting.
peg.ebnf: Update docs for peg change.
assocs.extras: adding delete-value-at.
python: new syntax PY-QUALIFIED-FROM, so you can import eg __builtin__:map and not have it clash with factors map
python: feature to create python callbacks/functions, now you can call hofs like map and reduce
python: fix a reference leak in the (>py) word
help.topics: make wrappers unwrap into links.
ui.gadgets.buttons: use hide-status on button-leave.
ui.gadgets.tables: show summary for mouse row or selected row.
libc: don't use unparse which requires prettyprint.
io.backend: Remove duplicate definition of file-mode. Add mkdir-mode using non-magic symbols. Cleanup imports.
io/ui: slim down the USE: list
jamshred: it lives again, now you can jam and shred!
images: cleanup using.
boids: removing unnecessary with-translation.
unmaintained: reanimated cairo demos, mostly working.
unmaintained: fix accessors (>>foo) should be foo<<.
unmaintained: restoring trails, which is a neat processing demo.