More docs, some UI tweaks to improve consistency
Minor release:
- Added position ranges to tree traversal. #232
- Changed default type for range arguments for VariantIterator and data matrix generation. #233
- Skipping fixations is now optional in :func:
fwdpy11.data_matrix_from_tables
. - The C++ back-end for population classes was changed to avoid deleting move constructors. #231
- Documentation updates