Add SQLAlchemy to intersphinx

There's some references here and there, the one for SQLShipMixin bothered me enough to do it.
Add .killmail API autodoc stuff

Only SQLShipMixin is documented right now, the other stuff will come later.
Fix a typo in killmail intro
Document pretty much the rest of the killmail API
Always include members in autodoc directives

Include 'special' method names as well.
Update killmail documentation for new SQL mixin

Also reword some areas, just some minor editing.
Fix the eve-marketdata link in killmail docs