Call package-initialize in sandbox
Add /sandbox to .gitignore
Add lib/hyperspec.el back into slime (closes #1665)
Merge pull request #1666 from m2ym/better-sandbox

Call package-initialize in sandbox
Add more info about building and testing recipes
Sandbox makefile target should depend on packages/archive-contents

See #1666
Add note about "make sandbox" (see #1666)
Extend note about sandbox target