Explore gojq instead of linking to libjq

[jzelinskie]

gojq is a pure Go libjq implementation. It does have documented incompatibilities, but it's worth leaving an issue open to see if the community is more interested in 100% compatibility or attempting to avoid the complication of linking against C.

[jzelinskie]

We could potentially then support various backends if we fleshed out an Engine interface that could be implemented by both libjq and gojq. We could compile all engines into all binaries or allow users to build without cgo and only use pure Go engines.