Add package 'Encodings'

[eine]

Coming from VUnit/vunit#588 and VUnit/vunit#595, the main purpose of this PR is to add the possibility to encode generic strings, in order to work around the limitations of some simulators which do not accept all the symbols.

This is achieved by adding a new package (Encodings). Currently, it contains functions b16encode and b16decode only. Nonetheless, it can be extended in the future to support other encodings such as base32 or base64. Precisely, the naming of the functions mimicks https://docs.python.org/3/library/base64.html.

A function named decode is used in jsonLoad to detect and decode the input, if required. As a result, users don't need to change their VHDL code to use new feature. Decoding is done before loading the JSON file. Hence, it is possible to encode the path to the JSON file, should any simulator have issues with \, /, :, etc. and should the length also be limited. The detection logic can be significantly improved: https://stackoverflow.com/questions/18419428/what-is-the-minimum-valid-json

A new testbench ( Examples/Encodings_VUnit.vhdl) is added, where encoding/decoding functions are tested independently from JSON features. Apart from that, example Boards_VUnit.vhdl is extended:

• Four tests are described: stringified JSON generic, b16encoded stringified JSON generic, JSON file path generic and b16encoded JSON file path generic.
• Procedures test_board0 and test_board1 are described. These can be potentially saved in a separate package, to be used in other testbenches.
• In the run.py file, from base64 import b16encode is used to encode the stringified JSON/object.

---

Apart from adding 'Encodings', since this projects has not been updated in 1.5y, I added other modifications to this PR:

• jsonLoadFile was merged into jsonLoad, but the former is still shown in the README and used in Boards2. It is fixed.
• Subdir 'Tests' is created and subdir 'vhdl' is renamed to 'Src'.
• The script to execute VUnit tests in a docker container is outdated. It is updated and it is generalized, in order to be used to run different tests/examples.
• Example Boards2 is updated to fix it after renaming/moving Tests/Src. Also, a shell script which is equivalent to the existing Boards.cmd file is added.
• A GitHub Actions (GHA) workflow is added, where Tests/VUnit and Tests/ghdl are executed.
• Travis CI is deprecated and .travis.yml is removed.

/cc @LarsAsplund @felixn

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[Paebbels]

When editing files to reflect the reviews above, please do also these minor changes:

• rename Src to src
• rename Tests to tests