(#132) Host javadocs in javadoc.io

[llorllale]

README: now including javadoc.io badge
pom.xml: now excluding javadoc from report generation in profile 'site'
index.md.vm and site.xml: JavaDoc links now pointing to javadoc.io

closes #132

[codecov]

Codecov Report

Merging #135 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #135   +/-   ##
=======================================
  Coverage   90.74%   90.74%           
=======================================
  Files          47       47           
  Lines         681      681           
  Branches       32       32           
=======================================
  Hits          618      618           
  Misses         55       55           
  Partials        8        8

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