Added full_mm

With examples and tests
Separate function to reconstruct mixing matrices

... and compute group sizes.
Tests plus examples
Removing tests for as.mixingm
Removing tests for mixingm
Commented old code, promoted new mixingm
Removing as.mixingm
Fixed methods for assort
Fixed coleman() for new mm computation
Fixes to segregation measures
Fixes in tests
Added function valid_mm
Fixes in assort
Removed TODO

Using Github issues
in README
Added default method for coleman

Various doc fixes.

Added test for coleman given contact layer of the mixing matrix and
group sizes.
Fixing E-I

Added default method that coerces object to table.
Added a test based on Catania.
Replaced array method with table method.
Trying to fix full_mm

Renamed examples as.mixingm to mixingm.
Added example of full_mm as a test.
Fixed full_mm and test for coleman
Fixed freeman

Changed method for arrays to tables.
Added default method that coerces to table.
Fixes in the documentation
Fixing mixingm, freeman and (partly) gamix

Creating default methods that coerce to tables.
Correcting documentation.