feature: configurable logging

[bobheadxi]

• Ego version (or commit ref): cd980ec

right now the library logs wherever it wants, which is rather annoying because:

1. if we have our own logging framework, standard out is now polluted by logs formatted differently
2. logs cannot be silenced, so in tests we have a nice mess of output from riot whenever a test fails

proposal:

• accept a minimal logger interface in Engine configuration
• provide a no-op logger by default

[bobheadxi]

@vcaesar I'd be willing to put in a PR to implement this

[stuchilde]

Did you resolved it?

[bobheadxi]

I ended up migrating to https://github.com/blevesearch/bleve, which IMO is a nicer library and supports setting a custom logger