Make gem binaries faster

[noteflakes]

When lyp is installed as a gem, gem binaries add an annoying additional latency of about 300ms. The only way to get rid of this latency is to rewrite the gem binary files. Lyp should detect that it's being used as a gem, and suggest the user run a builtin command to rewrite the binaries:

$ lyp -v
Lyp is being used as a ruby gem. To make the lyp and lilypond binaries faster, 
run the following command:

  lyp rewrite binaries

This message should be only displayed once.