Update packaging - #905

Changes:

1. Began transition to modern packaging standards (PEP 517 & 660) using the pyproject.toml file. I only moved what was absolutely necessary to avoid any issues. I'll statically define more metadata in the next PR.
2. Moved configuration for other tools into the pyproject.toml file.
3. Removed versioneer in favor of the de facto standard for integrating VCS metadata, setuptools-scm.
4. setuptools-scm modifies the default files finders to include everything tracked by Git so the MANIFEST.in file now defines exclusion rather than inclusion patterns.
5. The version file is now exclusively generated at build time and has been added to the .gitignore file.
6. Modified the .gitattributes file to use lf by default with explicit exceptions for Windows scripts like the make.bat currently used to build docs. Many folks working on Windows (such as myself) prefer to only work with LF and set the following:

   git config --global core.eol lf
   git config --global core.autocrlf input