Enable More C++ Warnings

[badisa]

Goal

• Enable C++ warnings to enforce more explicit behavior

Solution

• Select warnings to enable
• Likely should enforce warnings as errors
• Avoid these warnings for all vendored code

Proposed warnings

• As mentioned by @mcwitt -Wconversion is a good candidate based changes around #601

Originally discussed here: https://github.com/proteneer/timemachine/pull/608#issuecomment-1030135498