add client and move some network functions
add check for zero-length array in CalculateHash()
fix typo
Keeping consistent style of opening section.

Each paragraph starts with "Sia is ___."
Merge pull request #94 from mdznr/patch-1

Keeping consistent style of opening section.
Missing "is" in sentence "Sia secure."
Merge pull request #95 from mdznr/patch-2

Missing "is" in sentence "Sia secure."