Merge OEBIF

[JimmyCushnie]

As requested, this is a merge of Outline Effect But It's Faster, the fork I've been maintaining while cakeslice was away.

Changes:

• added a checkbox to the OutlineEffect component to disable the automatic enabling of all scene Outlines at startup. (#30)
• don't use GetComponent calls in OutlineEffect.OnPreRender (#38)
• only allow there to be one OutlineEffect camera
• enabling and disabling Outline components is much faster and produces much less garbage
• OutlineEffect.OnPreRender produces much less garbage
• OutlineEffect.OnPreRender returns immediately if there are no active Outlines in the scene
• added ability to install project via the Unity Package Manager
• reorganized project folder structure to something nicer
• various code improvements

It is notable that this PR does not include 781625e. There is some discussion on how best to merge this at OEBIF/#2.