Add a criterion listing to arsel --help

[RhysU]

Add a criterion listing to arsel --help:

    The model order will be selected using the specified criterion.
    Criteria are specified using the following abbreviations:
        AIC  - Akaike information criterion
        AICC - asymptotically-corrected Akaike information criterion
        BIC  - consistent criterion BIC
        CIC  - combined information criterion
        FIC  - finite information criterion
        FSIC - finite sample information criterion
        GIC  - generalized information criterion
        MCC  - minimally consistent criterion

[nicholasmalaya]

I would also request a '--version', perhaps set off of the github revision number, or a dot versioning system.