Updated gitignore

Ignore vim comment files, and the build folder (for out of source
builds)
Removed vim swap file

This was an accidental upload.
Fixed gitignore, made makefile cross platform.

Fixed gitignore to actually ignore vim swap files.
Cross platform makefile

The mkdir step, should now work on all platforms.
We want uniform line endings!

The gitattributes file, should ensure that files always have the same
line endings at checkout.
We want crlf endings
Moved clipper to a libraries folder.
Added a 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.
Merge pull request #76 from Skeen/master

out-of-source building + more