Add issue.remove_field_value()

[nickbroon]

Complements the existing add_field_value()

[adehad]

@nickbroon thanks for this! Do you think we can add a test (to: tests\resources\test_issue.py) where perhaps we

1. add the value (perhaps to the label field)
2. check the value is added
3. remove the value
4. check the value is removed
   ?

[nickbroon]

thanks for this! Do you think we can add a test (to: tests\resources\test_issue.py) where perhaps we

1. add the value (perhaps to the label field)
2. check the value is added
3. remove the value
4. check the value is removed
   ?

adehad, I pushed a update to the Pull Request that adds a test that exercises both remove_field_value() and add_field_value()