lame: update stable url format, add license

[samford]

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The stable URL for lame is using a format that isn't compatible with brew livecheck's Sourceforge strategy. This appears to be the only SourceForge URL that uses this different format. The others use a URL starting with https://downloads.sourceforge.net/project/ instead of https://downloads.sourceforge.net/sourceforge/.

This updates the stable URL to bring it in line with the other SourceForge URLs, while also making it compatible with livecheck's Sourceforge strategy.

[samford]

I added the license information from the COPYING file found in the lame SVN trunk here: https://sourceforge.net/p/lame/svn/HEAD/tree/trunk/lame/COPYING

[dtrodrigues]

Can this be made into a style check for future SourceForge URLs?

[samford]

Can this be made into a style check for future SourceForge URLs?

Yep, after I read your comment I worked on adding a couple cases to the existing urls RuboCops for SourceForge URLs and I'll create a Homebrew/brew PR for the changes tomorrow.