non explicit declarations block some compiling

[himwho]

On some platforms (windows visual studio) I run into compiling errors due to this chunk: https://github.com/mbientlab/MetaWear-SDK-Cpp/blob/master/src/metawear/dfu/cpp/file_operations.cpp#L120-L134

specifically these lines:

Error (active) E0350 more than one operator "=" matches these operands: src\metawear\dfu\cpp\file_operations.cpp 127

Error (active) E0350 more than one operator "=" matches these operands: src\metawear\dfu\cpp\file_operations.cpp 130

I am trying to figure out what the non-auto declares are for this function but because i do not use this function I am having a hard time recommending a PR to make this more explicit.