Issue133 parallel learning

[javiarrobas]

Fixes https://github.com/ibpsa/project1-boptest-gym/issues/133.

@Xiangwei this extends your pull request in https://github.com/ibpsa/project1-boptest-gym/pull/134 with the following:

• Inserts your functionality into Python methods to make it more modular.
• Moves the example with a vectorized environment to examples/run_vectorized.py as that is the convention.
• Modifies the testing environment to install PyYAML as that is needed to configure the vectorized environment.
• Implements a test that checks the functionality of the vectorized environment.
• Edits README.md and releasenotes.md accordingly.

Please let me know if you have any further suggestion. Otherwise I'll merge this PR.

[XiangweiW]

@JavierArroyoBastida , No further issues from my side. Thanks again for your work and for considering this PR!