Generate valid mix and textMD metadata

[tledoux]

Add unit test for all the outputs.
Fixes #219

[codecov]

Codecov Report

Merging #220 into integration will increase coverage by 2.19%.
The diff coverage is 94.11%.

@@                Coverage Diff                @@
##             integration     #220      +/-   ##
=================================================
+ Coverage          38.19%   40.38%   +2.19%     
- Complexity          3059     3124      +65     
=================================================
  Files                386      386              
  Lines              31321    31329       +8     
  Branches            6104     6105       +1     
=================================================
+ Hits               11962    12653     +691     
+ Misses             17188    16297     -891     
- Partials            2171     2379     +208

Impacted Files	Coverage Δ	Complexity Δ
.../edu/harvard/hul/ois/jhove/handler/XmlHandler.java	54.45% <94.11%> (+21.45%)	176 <0> (+21)	⬆️
...a/edu/harvard/hul/ois/jhove/NisoImageMetadata.java	68.06% <0%> (+7.92%)	154% <0%> (+24%)	⬆️
...in/java/edu/harvard/hul/ois/jhove/HandlerBase.java	66.32% <0%> (+10.36%)	45% <0%> (+9%)	⬆️
...java/edu/harvard/hul/ois/jhove/TextMDMetadata.java	64.28% <0%> (+11.22%)	22% <0%> (+10%)	⬆️
.../main/java/edu/harvard/hul/ois/jhove/Rational.java	100% <0%> (+14.28%)	7% <0%> (+1%)	⬆️

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[carlwilson]

Hi @tledoux, I've reviewed this and it looks straight forward, I'll be merging shortly when the updated build completes.