Update dependencies; handle stack separately; add location if available; support global shared context

[catobus]

This addresses the following issues:

• Update axios to fix recent vulnerabilities (ie SSRF). Update dependencies to align with a more recent log4js-node version.
• Do not concatenate the stack trace with the message; send it in a separate field.
• Send location data if available (ie file name, function name, line number).
• Add support for global shared context (similar to log4j MDC).
• Align tests, comments and readme.

Thank you!

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@0b1a225). Click here to learn what that means. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             master        #7   +/-   ##
==========================================
  Coverage          ?   100.00%           
==========================================
  Files             ?         1           
  Lines             ?        34           
  Branches          ?         0           
==========================================
  Hits              ?        34           
  Misses            ?         0           
  Partials          ?         0           

Impacted Files	Coverage Δ
lib/index.js	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 0b1a225...9935e11. Read the comment docs.

[catobus]

Finally all Travis builds are good to go!

[catobus]

@nomiddlename any chance you could take a look at this PR?

[sparklton]

just to chime in - it would be great if these changes are absorbed into the base