fix(message-handler): Rewire promise rejections as Error objects and

[mirceanis]

fixes #294

The actual fix is renaming the error event to ev_err instead of error.

During this fix, I also "standardised" the way errors are thrown or rejections called.
The bottom line is always use an Error object.
It makes things more consistent and also easier to test.

This will be enforced with a rule like no-throw-literal when we turn linting back on.

[codecov]

Codecov Report

Merging #300 (c7f932c) into beta (07fcb76) will increase coverage by 0.25%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##             beta     #300      +/-   ##
==========================================
+ Coverage   65.27%   65.53%   +0.25%     
==========================================
  Files          63       64       +1     
  Lines        1552     1555       +3     
  Branches      242      242              
==========================================
+ Hits         1013     1019       +6     
+ Misses        444      441       -3     
  Partials       95       95              

[simonas-notcat]

Looks good