Allow Strings and URIs for the @Link annotation when serializing

[andreas-repp]

With this PR, it becomes possible to use the @Link annotation with Strings and URIs making the library less intrusive and easier to use.

Code Example:

        @Link
        public String stringLink = "http://something.com";

        @Link
        public URI uriLink = new URI("http://something.else.com");

[codecov[bot]]

Codecov Report

Merging #27 into master will increase coverage by 0.25%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #27      +/-   ##
============================================
+ Coverage     77.27%   77.52%   +0.25%     
  Complexity       63       63              
============================================
  Files            10       10              
  Lines           352      356       +4     
  Branches         67       69       +2     
============================================
+ Hits            272      276       +4     
  Misses           72       72              
  Partials          8        8              

Impacted Files	Coverage Δ	Complexity Δ
.../jackson/dataformat/hal/ser/HALBeanSerializer.java	84.96% <100.00%> (+0.46%)	4.00 <0.00> (ø)

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[andreas-repp]

@langecode: Could you have a look at this PR?

[langecode]

..and again thanks for the contribution. I had not noticed your PR before the mention, sorry.