libreplaygain-r475-bp153.1.15

- Make descriptions more meaningful.

- More spec file cleanup:
  * Use SPDX identifier to License
  * Use https:// for Source and Url
  * Remove BuildRoot

- Add libreplaygain-math.patch: link with -lm.
- Use cmake macros.
- Move source modifications from %prep to %build. Makes 'quilt
  setup' more robust.
- Remove some unneeded comments from %install.
- Remove %defattr.. No longer needed.

- Correct version number to r475.

- Initial rpm release (version 20110810_r475).