woff2_compress does not allow to specify WOFF metadata

woff2_compress only accepts the input font file as argument and does not allow to provide metadata (especially http://dev.w3.org/webfonts/WOFF2/spec/#Metadata).

As a comparison, sfnt2woff has the following parameters:

```
fred@debian:~$ sfnt2woff
Usage:
sfnt2woff [-v .] [-m ] [-p ]
package OpenType as WOFF, creating .woff
Options:
-v . set font version number (major and minor, both integers)
-m include metadata from (not validated)
-p include private data block
```

See also https://lists.w3.org/Archives/Public/www-font/2015JanMar/0000.html