Added linear map function

Updated google test version

Updated include guards

Updated minimum CMake version to 3.14 to support FetchContent_MakeAva…

…ilable

Updated directory structure to support Arduino in addition to CMake b…

…uilds

Updated version of Eigen

Added static assert to only support floating point types

Updated to use std::span, so only 1 version of polyfit and polyval ne…

…eds to be maintained

Fixed the const-ness of the C style polyval

Updated namespace to bfs