Fix Graph.get_out_degrees() and Graph.get_out_degrees()

This also adds the missing Graph.get_total_degrees() and missing
documentation.

This fixes issue #596
4 jobs for master in 511 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #4071
amd64
job_clang_amd64

08:30:55

failed #4073
amd64
job_clang_amd64_nosh

08:30:47

failed #4070
amd64
job_gcc_amd64

08:30:52

failed #4072
amd64
job_gcc_amd64_nosh

08:31:04

 
Name Stage Failure
failed
job_gcc_amd64_nosh Test
   4 tests in gt_format
4 tests in 1 items.
4 passed and 0 failed.
Test passed.

Document: generation
--------------------
Terminated
ERROR: Job failed: exit status 1
failed
job_clang_amd64 Test
<string>:1: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`).
<string>:1: UserWarning: tight_layout : falling back to Agg renderer
<string>:1: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`).
<string>:1: UserWarning: tight_layout : falling back to Agg renderer
<string>:53: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`).
<string>:53: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`).
<string>:1: RuntimeWarning: More than 20 figures have been opened. Figures created through the pyplot interface (`matplotlib.pyplot.figure`) are retained until explicitly closed and may consume too much memory. (To control this warning, see the rcParam `figure.max_open_warning`).
Terminated
ERROR: Job failed: exit status 1
failed
job_gcc_amd64 Test
   3 tests in scalar_assortativity
53 tests in 6 items.
53 passed and 0 failed.
Test passed.

Document: generation
--------------------
Terminated
ERROR: Job failed: exit status 1
failed
job_clang_amd64_nosh Test
  80 tests in default
80 tests in 1 items.
80 passed and 0 failed.
Test passed.

Document: generation
--------------------
Terminated
ERROR: Job failed: exit status 1