Relicense to LGPL 2.1, MIT, or Apache 2.0

I'd like to relicense to LGPL 2.1, MIT or Apache 2.0.

This should hopefully work around ambiguities of whether crates linking with this one have to be open source.

Right now it looks as if crates that depend on this one might have to make themselves available in object form to allow for relinking. As the crate author, I wouldn't enforce this, but it understandably has people jumpy.

I only picked LGPL 2.1 a) to be compatible with speech-dispatcher and b) because I didn't realize this potential complication. Given that it dynamically links to speech-dispatcher, I don't know that the license needs to be LGPL to be compatible. I'm keeping it for now, as to not further complicate existing licensing.

What say you, @MallocVoidstar?