READY: Resolve "C++17 support"
This MR moves GekkoFS to C++17 with the following replacements:
- CMake modifications
- Replacing
boost::filesystemandboost::optionalwithstd::filesystemandstd::optional, respectively - Using nested namespaces
- Using
if constexpr
Depends on merge of !66 (merged).
Closes #134 (closed)
Edited by Marc Vef