add Info data structure to better manipulate the configuration

to run benchmark, we need to manipulate the parameters, so we add a new Infos module to represent the configuration and easy manipulation.

this release was done before a major change.
I'll change the Key-value Store to pointing to the layer path rather than the specific mip level. the design was inspired by cloud-volume. This design will allow more advanced features in the future. The future change will break some code, so this is the last backward compatible release.