Add second MIT license text and add SPDX tag in all files

[superna9999]

In order to help pyamlboot beeing used in more projects, I'll propose to add a second license which is more compatible with other licenses like the GPL2 licence.

Note this dual licensing will only be valid when merged in the https://github.com/superna9999/pyamlboot master branch.

The https://github.com/bootlin/snagboot maintainer/developer asked me relicensing, I already provided an older version (https://github.com/superna9999/pyamlboot/tree/v1.0-mit-partial-relicense) with only my authorship with SPDX tag on PROTOCOL.md and pyamlboot/pyamlboot.py, but I think it would be better to have the whole source code and text using this dual license.

Acks needed for relicensing:

• [x] @jeromebrunet
• [x] @tchebb
• [x] @JulienMasson

Would you give your ack for such relicensing ?

[tchebb]

Yes, relicensing to MIT is fine by me.

[jbrun3t]

Sure

[massonju]

sure

[superna9999]

Thanks for acking! LGTM