Add new function launcher

[mcopik]

While FMI supports launching a swarm of function workers, we have used some Bash scripts to launch many functions in parallel. We need a proper tool similar to mpiexec that would take parameters such as the number of functions, name of the function, and cloud region, generate a configuration for each function, and quickly launch a desired number of workers.

• Implement a basic parallel launcher supporting arbitrary functions.
• Document the input format describing the function ID and the hierarchy of workers (see Implement shared-memory communication #7).
• Add a local backend to start functions as Docker or native processes on the same system.
• Add error handling to display failure outputs from functions.
• Add a tree-based launcher to achieve a logarithmic startup time.