added 'make' docs, filled out whitepaper

Calling 'make' now compiles the whitepaper using pdflatex, which is
distributed with texlive. Calling 'make docs' only compiles the
whitepaper.

Added a section to the whitepaper about dishonest blockchains.
Added a section explaining the storage layout of Sia.
Rewrote the proof of access section
Wrote a proof of storage section
Allocated space for 'The Problem of Delegation'
Allocated space to explain what a complete heartbeat looks like.
Merge branch 'master' of github.com:Siacoin/Sia
Don't build docs by default, fix for travis-ci