Renamed MetricalHierarchy to Meter.
Renamed MetricalKernel to MetricAccentKernel.
Renamed two timesignaturetools to match recent nomenclature changes.

    timesignaturetools.establish_metrical_hierarchy()
    timesignaturetools.fit_metrical_hierarchies_to_expr()

    ==>

    timesignaturetools.rewrite_meter()
    timesignaturetools.fit_meters_to_expr()