Address conversion and initialization warnings on MSVC

[hobu]

This one requires #49 to see the resulting output, but it addresses a number of warnings that recent MSVC complains about. Please review them carefully if you decide to merge them. It is possible these casts are incorrect, but there is no way for me to verify data integrity because there are no tests.

Can we please have some tests? 😄

Howard

[hobu]

This PR (and the v2.1.0 release) was failing due to the cli_utils not having C++17 enabled.

D:\a\spz\spz\src\cc\splat-types.h(56): error C2429: language feature 'structured bindings' requires compiler flag '/std:c++17'
D:\a\spz\spz\src\cc\splat-types.h(218): error C2429: language feature 'structured bindings' requires compiler flag '/std:c++17'
D:\a\spz\spz\src\cc\splat-types.h(219): error C2429: language feature 'structured bindings' requires compiler flag '/std:c++17'

Does the project intend to support windows/MSVC?