Update code to run under Python3 + Conda packaging

• Updated to work with Python 3
• Added unit tests to ensure basic functionalities of refscrub
• Updated list of platform specific dependencies to be installed when installing refscrub in dev mode (see setup.py)
• Installed and tested refscrub against Python 3.[6,7,8] using tox
• Formatted Python code to conform to the PEP8 style guide
• Created conda package for refscrub that can run on Python 3.[6,7,8]
• Updated .gitlab-ci.yml to run a linter and unit tests for Python 3.[6,7,8] in GitLab CI pipeline

conda.recipe/meta.yaml

 package:
   name: refscrub
-  version: 2011.046
+  version: 2020.216
 
 source:
-  path: ..
+  path: ../
 
 build:
-  # If the installation is complex, or different between Unix and Windows, use
-  # separate bld.bat and build.sh files instead of this key.  Add the line
-  # "skip: True  # [py<35]" (for example) to limit to Python 3.5 and newer, or
-  # "skip: True  # [not win]" to limit to Windows.
-  script: python setup.py install --single-version-externally-managed --record=record.txt
+  noarch: python
+  number: 1
+  script: {{ PYTHON }} -m pip install . --no-deps -vv
 
 requirements:
   build:
-    - python
-    - setuptools
+    - python >=3.6
+    - pip
   run:
-    - python
+    - python >=3.6
+
+test:
+  source_files:
+    - tests
+  commands:
+    - python -m unittest
 
 about:
   home: https://git.passcal.nmt.edu/passoft/refscrub
+  license: GPLv3
+  license_file: LICENSE
   summary: Remove select packets from RT130 data