Use absolute URI in CODE_OF_CONDUCT

sphinx (at least the version used by readthedocs) appears to interpret <http:contributor-covenant.org>`__ as http://khmer.readthedocs.org/en/v1.2/dev/contributor-covenant.org.  Using an absolute URI (despite this format appearing in the restructuredText documentation) should fix this.

github appears to render it fine, however...
added test to import all sandbox scripts w/o executing them; see #707
fixed import of all .py scripts in sandbox/
added exec test for all sandbox scripts
added main()
skip sandbox scrip tests in distro
ChangeLog entry for some sandbox testing/cleanup
use temp filename, not curdir
PEP8
Merge branch 'fix/test-tempfiles' of github.com:ged-lab/khmer into update/sandbox

Conflicts:
	ChangeLog
Merge pull request #710 from ged-lab/fix/test-tempfiles

use temp filename, not curdir
Merge branch 'master' of github.com:ged-lab/khmer into update/sandbox
fixed PEP8
Merge pull request #709 from ged-lab/update/sandbox

Added testing to make sure all sandbox scripts are import-able and execfile-able.
give SeqAn credit
don't list specific SeqAn scripts
Merge pull request #712 from ged-lab/feature/seqan-citation

give SeqAn credit
Merge pull request #684 from jsspencer/master

Use absolute URI in CODE_OF_CONDUCT
added tests:
	test_abundance_dist_single_nosquash()
	test_abundance_dist_single_savetable()
	test_filter_abund_2_singlefile()
adds test coverage towards issue 386, plus additional general test
coverage
added load_into_counting_multifile() test