Updated Analysis Proposal

Analysis Proposal
<https://docs.google.com/document/d/1kx62tpy5hGIbHh6tHMAryon9Sgye--W_IsHTeCMlmEo/edit?usp=sharing>

I've made some updates to the analysis proposal based on feedback from the
working group. Notable updates:

   - Added some thoughts on a possible cost function, which would replace
   looking at the 95th percentile of the network delay distribution.
   - Added a section mentioning that we should try using a page view to
   multiple family style input.
   - Updated the section on the font test corpus to more specifically call
   out that we'll want fonts outside of the Google Fonts collection.

Please review and share your thoughts.