Update freud.box periodic

[Eric Harper]

Currently there is no way to set the periodicity of a box at the python level (and even at the C++ level it's non-intuitive). It shouldn't be difficult to do this, but it needs to be done.

[Vyas Ramasubramani]

Merged in issue-129 (pull request #141)

Issues 129 and 137

Resolves Issue #129 Resolves Issue #137

Approved-by: Vyas Ramasubramani [e-mail]

→ <<cset a2df6b17d381>>

[Vyas Ramasubramani]

Merged in issue-129 (pull request #141)

Issues 129 and 137

Resolves Issue #129 Resolves Issue #137

Approved-by: Vyas Ramasubramani [e-mail]

→ <<cset a2df6b17d381>>