* ogi.el (ogi--project): New "internal" variable.
(ogi-insert-entry): Add `GH_PROJECT' property to identify which
github property an entry came from. Only add a `MILESTONE' property
when it has a name (as in, when it exists). Add a `DEADLINE' to the
entry if the milestone has a due date.
(ogi-get-for): Rename from `ogi-insert', which is kind of
non-descript. Bind `ogi--project' to whichever project we're
fetching so other functions can use it.
