Execute pipeline via config file

[ipurusho]

In addition to command line execution (#8), allow user to input one config file (tab delimited, yaml, etc). Config file must be flexible for different tools and their varying input.

[lishen]

I just mentioned that in other issues. You may need multiple configurations: a global configuration to setup the execution environment, a per-project configuration and multiple configurations for each of the tools, such as short read aligners.