cmake, SWIG: Minimum 3.0.0
INSTALL-Docs: Requires SWIG >=3.0.0
Merge pull request #20 from lclc/swigMinimum

Swig minimum 3.0.0 cmake check & docs update
CMake: fix protobuf include path on OS X

include_directories() should be executed for all platforms.
find_package(Protobuf) can be removed since it's executed in the
top-level CMakeLists.txt.
Merge pull request #22 from toxeus/fixMacCompile

CMake: fix protobuf include path on OS X
cppcheck: fix variableScope
Merge pull request #21 from toxeus/fixScope

cppcheck: fix variableScope
LogStream conversion of opentxs-script main.cpp