Github Actions, small fixes, allow specifying endpoint for testing, wrap secret keys

[thalesmg]

Hi! Thanks for creating this library! :beers:

While exploring the library, I found a few issues that are hopefully fixed, and I took the opportunity to add support for Github Actions (and I assume that Travis is no more) and some smoke integration tests for blob storage.

• Adds basic github CI
• Fix error parsing
• Fix generation of string to sign when content length is zero
• Allow specifying custom endpoint for testing (fixes https://github.com/dkataskin/erlazure/issues/39)
• Add smoke tests for blob storage operations
• Wrap keys to avoid accidental printing on crashes

[dkataskin]

Thank you!

[thalesmg]

Thanks for reviewing and accepting! I have a couple more fixes to follow up. :smiley_cat: