ENH ResultsReader supports Serpent 2.2.0

[drewejohnson]

Closes #467

For bug fixes and enhancements, link to the corresponding issue.

Make sure you have read over the developer guide to ease the review process. These include:

• [x] PR fits the project scope
• [x] Code to be committed is DRY and matches the code style of the project
• [x] New and/or changed features are well documented and have adequate testing
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[drewejohnson]

@DanKotlyar and/or @aalfonsi can you check if the version string in the 2.2 result file is 2.2.0 or 2.2. I don't have the new version on my personal laptop to check

[drewejohnson]

Draft until #470

[DanKotlyar]

We don't have the new version yet so I don't know whether it is 2.2.0 or 2.2

[aalfonsi]

@DanKotlyar and/or @aalfonsi can you check if the version string in the 2.2 result file is 2.2.0 or 2.2. I don't have the new version on my personal laptop to check

2.2.0

[aalfonsi]