Hierarch helper

[attipaci]

Make it easier to create HIERARCH-style header keywords, by hiding the internal naming convention for such keys from users, who can instead just create the long or hierarchical FITS keywords they desire. Users can just ise one of the static Hierarch.key() methods to constructs HIERARCH-style keywords for use within this library. E.g.:

  String key = Hierarch.key("myLongFitsKeyword");

which sets key to HIERARCH.myLongFitsKeyword (which is how we refer to this long keyword within the library, such as with header access methods).

or:

  String key = Hierarch.key("my.hierarchical.fits.keyword");

to set key to HIERARCH.my.hierarchical.fits.keyword, or equivalently to the one above:

  String key = Hierarch.key("my", "hierarchical", "fits", "keyword");

The resulting string can be used as the non-standard keyword in the library's header access methods.

[codecov]

Codecov Report

Merging #458 (481b850) into master (abb6eab) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #458   +/-   ##
=========================================
  Coverage     97.58%   97.58%           
- Complexity     4702     4705    +3     
=========================================
  Files           205      206    +1     
  Lines         13565    13571    +6     
  Branches       2094     2095    +1     
=========================================
+ Hits          13237    13243    +6     
  Misses          124      124           
  Partials        204      204           

Flag	Coverage Δ
unittests	97.58% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
...in/java/nom/tam/fits/header/hierarch/Hierarch.java	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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