chore: remove update script

Patches are floated in the master branch, and running
update-from-mozilla-central here would undo all that hard work.

Instead, updating should be done in the "upstream" branch.

This commit removes the update script from the master branch, so nobody
will be tempted to run it here.
chore: add .gitignore
spidermonkey: fix vs2010 build
spidermonkey: fix non-standard #if expression
config: add stuff js-config.h
build: add gyp build scripts
chore: add README.md

Clearly inspired by Ben's work.
Merge branch 'upstream'