Add beatx tool

[WolfgangDrescher]

In order to be able to create annotations for scores in VHV and verovio faster with beat values for certain moments on certain beats, I have created the basic functionality of humextra beat for humlib as beatx. Since humlib already has meter I only implemented the missing functionalities.

In terms of functionality, it is a mixture of the meter and the humextra beat program. For the formatting of the numbers I also use the HumNum::printTwoPart notation as with meter. Float values can be activated with -f instead.

Spine splits are currently not supported. The first token found for a track is used.

Options are:

s|spine-tracks|spine|spines|track|tracks=s   process only the specified spines
k|kern-tracks=s                              process only the specified kern spines
d|duration|dur=b                             display duration for each slice
u|beatsize|rhythm=s:4                        beatsize (recip rhythmic value); default=4
f|float=b                                    floating-point beat values instead of rational numbers
D|digits=i:0                                 number of digits after decimal point
c|comma=b                                    display decimal points as commas
t|tied|ties=b                                show beats of tied notes
r|rest=b                                     show beats of rests
full=b                                       show numbers on each slice