Fixes #1839 : Badge improvements in README.md

[proski]

*  Fixes #1839 : Badge improvements in README.md
   
   Use shields.io badge for Bintray, as the Bintray hosted badge shows
   "Download" and cannot be made to show "Bintray".
   
   Split an excessively long line for the first row of badges.
   
   Update the alt text for "Release Notes". Non-graphical users would only
   see a link to the release notes.
   
   "Javadoc" was misspelled as "Javadocs".
   
   Use HTTPS for all links.
   
   Use direct links to the package on Maven Central and Bintray.
   
   Use the default color for Javadoc, red looks as an error.

[proski]

Please compare:
Before: https://github.com/mockito/mockito/blob/release/3.x/README.md
After: https://github.com/proski/mockito/blob/badges/README.md

[codecov-io]

Codecov Report

Merging #1840 into release/3.x will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             release/3.x    #1840   +/-   ##
==============================================
  Coverage          86.71%   86.71%           
+ Complexity          2492     2489    -3     
==============================================
  Files                311      311           
  Lines               6551     6551           
  Branches             822      822           
==============================================
  Hits                5681     5681           
  Misses               674      674           
  Partials             196      196

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[TimvdLippe]

Again only 1 nit. Thanks 😄

[TimvdLippe]

Same as on the website PR, let's keep this mockito-development and fix the bug in Shipkit instead.

[proski]

OK, I've reverted that change. Sadly, it means that #1839 is not going to be fully fixed by this PR. At least "Download" would become "Bintray", so that users won't expect it to the the download link.