BENCH: add conjugate gradient benchmarks
BENCH: improve conjugate gradient solve benchmark
BENCH: restore a commented out line
MAINT: drop numpy 1.5 compatibility code in sparse matrix tests
Merge pull request #4306 from argriffing/add-cg-benchmark

Add benchmark for conjugate gradient solver.
BUG: make sparse conjugate gradient benchmark, added in gh-4306, run.
Merge pull request #4315 from argriffing/check-differential-entropy

MAINT: drop numpy 1.5 compatibility code in sparse matrix tests
TST: a few changes like self.assertTrue(x == y, message) -> assert_equal(x, y)
TST: in test_signaltools, changes like self.assertTrue(x == y, message) -> assert_equal(x, y)
Merge pull request #4320 from argriffing/test-assertion-syntax

TST: a few changes like self.assertTrue(x == y, message) -> assert_equal(x, y)
Merge pull request #4322 from argriffing/test-assertion-syntax-c

TST: in test_signaltools, changes like self.assertTrue(x == y, message) -> assert_equal(x, y)
MAINT: some fixes for stats.wishart added in gh-4135.

Fix docstring formatting and use np.linalg.slogdet where indicated by TODOs.
TST: clean up stats._multivariate tests a bit.
DOC: add stats.wishart/invwishart to 0.16.0 release notes.

[ci skip]
BUG: stats.wishart: fix issue with using floats for size arg to numpy funcs.

This raises DeprecationWarning's with recent numpy; should clearly be ints.
BUG: stats.wishart: fix test failure due to two variants to calculate logdet(x)

These are subtly different:

    In [46]: 2 * np.sum(np.log(linalg.cholesky(scale, lower=True).diagonal()))
    ...      - np.log(np.linalg.det(scale))
    Out[46]: 8.8817841970012523e-16

Use of ``np.linalg.slogdet`` is preferred.  Related change in gh-4313.
MAINT: document in stats.distributions when to stop special casing np.vectorize

Closes gh-4314.