Docs/log/log clean up (#591)

* • System
  - show_graph():
    fixed bug producing empty image for graphs with just one Mechanism
    added auto-recurrent projections

* • Log
  - added numpy_array output method

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* • Log
  - fixed bugs preventing logging during INITIALIZATION

* • Log
  - fixed bugs preventing logging during INITIALIZATION

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* • Log
  - logged_item, print_entries:  corrected to use 'value' rather than owner's name in reports

* • Log
  - logged_item, print_entries:  corrected to use 'value' rather than owner's name in reports

• Tests
  test_log:  added test_log_initialization

* • Log
  - _alias_owner_name:  added to used 'value' rather than owner's name in reports
  - nparray: bug fix to handle None values

• Tests
  test_log:  added test_log_initialization

* • Log
  - log_value: added

• Tests
  - test_multilayer: added test of log_value

* • Log
  - log_value: implemented
  - logged_item, print_entries:  corrected to use 'value' rather than owner's name in reports

• Tests
  - test_multilayer: added test of log_value

* • Log
  - log_value: implemented
  - logged_item, print_entries:  corrected to use 'value' rather than owner's name in reports

• Tests
  - test_multilayer: added test of log_value

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* • Log
  nparray(): fixed bug in which crashed if no log_entries

* • Log
  nparray(): fixed bug in reporting time in nparray output

* • Log
  docstring: fixed examples to reflect implementation of time field

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* • Log
  - nparray(): fixed bug in handling of duplicate of time values
  - docstrings: examples updated for print_entries, csv and nparray outputs

* • Log
  - nparray(): fixed bug in handling of duplicate of time values
  - docstrings: examples updated for print_entries, csv and nparray outputs