Return success from string queries

[askeksa]

Return success from plugin string queries. Otherwise some hosts (e.g. Renoise) may ignore the returned string.

[Boscop]

#41 Due to lack of maintainer activity (#38), we've decided to make a hard fork of this repo so we can continue active development: https://github.com/rust-dsp/rust-vst

Our fork has been worked on a lot. We eliminated memory allocations in the audio thread etc.
We would appreciate if you could open the PR on the new fork.

Also, we invite you to join our telegram group :)