add SendFile()
add test for SendFile()
Merge pull request #83 from lukechampine/node

SendFile
change "file" and "slice" to "segment"
Merge pull request #84 from lukechampine/node

Incorporate vocabulary changes
replace 'main' with 'server', and add testing
Merge branch 'master' into server
make 'participant' non-exported
add consts for message types
code-reveiw and clean state.go
move responsibility for tickLock to Start()
organization
switch message types to iota, clean up previous commit
reorganize announceSignedHeartbeat
finish organizational changes
delete main and test code
rename MessageSender and add a member function
update node for new MessageRouter
update quorum for new MessageRouter
add SetAddress() method to MessageHandler