Change doctests from print to assert statements

Address issue #109

The doctest tests in stats.py and discrete.py were changed from print
statements to assert statements. In test.py that needed a simple change to the
dimensions used in the assert statement. All three files had slight style
modifications to be in line with PEP8 standards.
Update elasticity notebooks to BCs and diff plots.

Address issue #105

Update elasticity notebooks to have the correct boundary conditions and added
plots to show the difference between the MKS and finite element strain
fields.
Merge branch 'issue-109-doc-test-assertions'

Fix #109
Merge branch 'issue-105-update-notebooks'

Fix #105
Update Github link to point at openmaterials

Address #94

The link was pointing at wd15, which no longer hosts the pymks site.
Remove redundant m_h equation on front page

Address #91
Delete redundant notebooks

Address #95

Including notebooks that are not finalized or complete or are just for
testing and diagnostics is confusing to users looking through the
notebooks. All the notebooks that are not included in the
documentation are now deleted. The Polynomials notebook looks like it
was used to implement the Legendre basis functions, which is now
complete. It evidently isn't finished yet. If a developer wants any of
these notebooks they should branch from the commit before this one and
maintain that branch on their own site.
Merge pull request #115 from wd15/issue94

Update Github link to point at openmaterials
Merge pull request #116 from wd15/issue91

Remove redundant m_h equation on front page
Merge pull request #117 from wd15/issue95

Delete redundant notebooks