Improves conan.io build configuration
Improves conan.io build configuration

- Depends on gtest as a static library (since it produces compiler
warnings as a shared library).

- Organizes and comments on conanfile.py to explain what is going on
clearly and differentiate between configuration to build oomuse-core
itself vs. configuration for clients to depend on it.

Lindurion/oomuse-core,Lindurion/oomuse-core