update ConstantFunctionByRegion.get_constants() to use Region.get_cells()
rename sfepy/fem/ -> sfepy/discrete/fem/
move general files from sfepy/discrete/fem/ to sfepy/discrete/
update setup.py files for new paths
split fem/dof_info.py -> common/dof_info.py, fem/lcbc_operators.py
update sfepy/discrete/__init__.py, sfepy/discrete/fem/__init__.py
update sfepy/ for new paths
update top level scripts for new paths
update examples for new paths
update tests for new paths
update scripts for new paths
update docs for new paths

- sync module index of developer guide with current sources
update docstrings for new paths
update MANIFEST.in for new paths
require integral argument in Approximation.describe_geometry()

- update FieldVariable.get_element_diameters()
make Region.create_mapping() a standalone function create_mapping()

- update docstring
- update get_physical_qps()
fix Region.iter_cells() for subdomains
add cell_offsets attribute to Domain, use it in Region

- simplify Domain.get_cell_offsets()
move fem/region.py -> common/region.py
new Domain.get_evaluate_cache()