newt target cmake <target> generates incorrect files for cmake on Windows

[kasjer]

When newt is executed on Windows like this:
newt target cmake my_target
it generates files that have Windows style separator \ in paths of properties ARCHIVE_OUTPUT_DIRECTORY, LIBRARY_OUTPUT_DIRECTORY and RUNTIME_OUTPUT_DIRECTORY.

cmake does not handle this correctly it works if paths backslashes are replaced with slashes.
paths like C:/msys64/home/... work fine while C:\msys64\home\... do not.