Key exchange
Create preshared keys and private keys.
Merge branch 'jake'

Conflicts:
	lib/share.rb
Reduce length of access codes
Fix key exchange
First working file sync
Add basic integration test
Reduce RSA key size

4096-bit keys are very costly.  Since they are only used for signing,
and not for encryption of data, they do not need to be future proof.
Add list of currently known security issues
Scanner now uses share path methods
Scanner test no longer stubs share
Merge branch 'jake'
Improve basic integration test
Fix basic integration test process launching
Request next file when a file is received
Fix multiple file sync
Fix scanner test
Write to intermediate file
Add another test to integration test
Add other input for share mode