Example models

[himoto]

• Create a function copy_to_current
• Update example code
• Update tests

[himoto]

The pull request #227 adds copy_to_current function, by which you can execute example models without cloning biomass.

from biomass import create_model
from biomass.models import copy_to_current

copy_to_current('nfkb_pathway')  # then you'll get nfkb_pathway/ in the current working directory.
model = create_model('nfkb_pathway')