out-of-source building

Now building out-of-source, to avoid pollution of source directory, promote support for multiple build targets, easier cleaning, and such.

I've added a .gitattributes file to ensure consistency regarding line endings, for source files.

I've extended the .gitignore to exclude the out-of-source build folder, vim tmp files, and the NUL error redirection file.

Moved clipper to a libraries folder (libs):
Added a libs/DO_NOT_CHANGE_THESE files, nothing developers that the sources in this folder, is not to be changed directly in this repository, but should rather be modified in their respective repositories.
Updated the Makefile to build this library.
Updated the Makefile to include the libs folder, as a isystem include
    I.e. do not throw errors, warnings, ect. from these headers.
Updated intpoint, and polygon to include clipper via. compiler lookup.

NOTE: Github seems to be doing funny business on some of the moved files. I've been unable to fix this, and my local diff is blank, the file program reports same line endings, ect.