switch from absolute tolerance to relative?

[golobor]

according to the code, currently, tolerance is specified in the units of #contacts.

An attempt to trace units:
line 135: margs are in the units of #contacts (i.e. proportional to # of reads in the library)
line 145: nzmargs are in the units of margs (#contacts)
line 156: var in the units of nzmargs (#contacts)
line 167: tol is compared to var

importantly, margs are re-computed using biases, but biases average out to 1.0, so margs first come out in the units of #contacts

Specifying tol in relative units makes more sense since it is hard for the user to know the # of reads in the library before balancing. We can still keep the option to specify an absolute tolerance, but I would argue that relative tolerance is a better default.

[golobor]

bump?

[golobor]

bump

[nvictus]

See #210