message: clean up windows build doc
diff: - Get binary dependencies (libamcl*, openssl, libsodium, libzmq, sqlite3).
  - Put all *.{lib,dll} into one directory and headers into include/ subdirectory.
  +- open MSVS development console
  +- execute "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
  - Point path to this directory using environment variables:
  - set SOVRIN_PREBUILT_DEPS_DIR=C:\BIN\x64
  - - set SODIUM_STATIC=y
  - set SODIUM_LIB_DIR=C:\BIN\x64
  - set OPENSSL_INCLUDE_DIR=C:\BIN\x64\include
  - set OPENSSL_LIB_DIR=C:\BIN\x64
  - set LIBZMQ_LIB_DIR=C:\BIN\x64
  - set LIBZMQ_INCLUDE_DIR=C:\BIN\x64\include
  -- open MSVS development console
  -- execute "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
  -- change dir to sovrin-client and run
  - - "cargo test" or
  - - cargo test --release --target x86_64-pc-windows-msvc
  +- set static flag for libsodium build
  + - set SODIUM_STATIC=y
  +- change dir to sovrin-client and run cargo (you may want to add --release --target x86_64-pc-windows-msvc keys to cargo)
  