Allow unpack in lambda-supporting sections, e.g. in params section

[iromeo]

Seems is working:

shell.executable("bash")

def get_params(wildcards):
    return {'test': 'oo', 'norm': 'oo'} 

rule test: 
    output: "aa"
    params: unpack(get_params)
    shell:  "echo {params}"