Merge pull request #159 from DavidVorick/upload

Fix MerkleCollapse
change atoms to a uint16
print wallet weight
prepend all client inputs with signature
Merge pull request #160 from lukechampine/client

Client signatures
touchups to the client-cli code
get siblings in UploadFile
begin implementation of the client struct
Merge branch 'master' into upload
add Init() to client
add type Keypair to siacrypto