generate and install a cmake configuration file

[xq-meng]

This change enables downstream cmake projects to automatically discover and consume repidcsv via find_package
Downstream projects can simply link against the imported target

target_link_libraries(my_target PRIVATE rapidcsv::rapidcsv)

This change is made as a follow-up to Discussion #125.

[d99kris]

Hi @xq-meng - thanks for contributing! The patch looks good to me. I will pull it to an integration branch where I'll add some example / documention, before merging it to rapidcsv master.

[d99kris]

This has now been integrated into rapidcsv master via 3aa768a.