Fix Cython and Numpy deprecations and match modern usage

[joefowler]

Original report by Joseph Fowler (Bitbucket: joe_fowler, ).

---

• Tell Cython to use Python 3 as its target.
• Numpy has deprecated the numpy symbols int, float, and bool, which have long been synonyms for the Python builtins.

‌

[joefowler]

Original comment by Joseph Fowler (Bitbucket: joe_fowler, ).

---

See https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations for info on the Numpy deprecation.

[joefowler]

Original comment by Joseph Fowler (Bitbucket: joe_fowler, ).

---

Fixed by PR 159.

[joefowler]

Original comment by Joseph Fowler (Bitbucket: joe_fowler, ).

---

Removing milestone: v0.7 (automated comment)