SKLL Release 2.1

[desilinguist]

This PR:

• Updates version number in version.py.
• Updates conda recipe and README.
• Updates release process document to include the conda and testpypi tester steps.
• Updates version number in tutorial output in documentation.

To review:

1. Review the changes in the PR.
2. Create a conda environment and test out the conda package with some of your SKLL experiments.
3. Let me know if I missed updating anything in the documentation.

NOTE: The pre-release test builds for both Conda and TestPyPI pass successfully 🎉.

[codecov[bot]]

Codecov Report

Merging #597 into master will not change coverage by %. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #597   +/-   ##
=======================================
  Coverage   95.06%   95.06%           
=======================================
  Files          20       20           
  Lines        2977     2977           
=======================================
  Hits         2830     2830           
  Misses        147      147           

Impacted Files	Coverage Δ
skll/version.py	100.00% <100.00%> (ø)

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