Releasing 0.6.0

Skipping a test that segfaults only on 1.5.0 and 2.0.0.  The test was
test_NR_DEC_issue188_beach_64bitsbox_jp2_41_decode.  It was not introduced
until the 2.1.x series and the fix was backported to 2.0.1.

glymur.test.test_jp2k.TestJp2k.test_no_cxform_pclr_jpx was failing on
1.5.2 only.  It's a pretty obscure test, so just skipping it on that
release.

Some tests for warnings are being skipped.
Merge branch 'master' into devel
Reworked warning tests, closes #245.

Using 3.x warning infrastructure to verify warnings.  Using old 2.x
infrastructure to suppress warnings when the point of the test is not
the warning itself but something else.

All tests for warnings moved into glymur.test.test_glymur_warnings.
Merge branch 'issue245' into devel