Added new selectortools functions.

    selectortools.selects_all_but_first_logical_tie_in_pitched_runs()
    selectortools.selects_all_but_last_logical_tie_in_pitched_runs()
    selectortools.selects_first_logical_tie_in_pitched_runs()
    selectortools.selects_last_logical_tie_in_pitched_runs()
    selectortools.selects_pitched_runs()

These functions configure and return selectors, analogous to the various
functions found in timespantools.
Merge branch 'master' of github.com:Abjad/abjad