Experimental named field support in tsv-summarize

[jondegenhardt]

This PR is a follow-on to PRs #284 and #285. It adds named field support to tsv-summarize. It works the same way as the support added to tsv-select, see PR #284 for more info.

Named field support is backward compatible with numeric fields. As with tsv-select and tsv-filter, this support is not documented yet, even in the help text. Documentation will be added when named field support has been added to all tools and a release performed.

This is a step towards enhancement request #25.

[codecov-commenter]

Codecov Report

Merging #286 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #286   +/-   ##
=======================================
  Coverage   99.32%   99.32%           
=======================================
  Files          18       18           
  Lines        6523     6556   +33     
=======================================
+ Hits         6479     6512   +33     
  Misses         44       44           

Impacted Files	Coverage Δ
common/src/tsv_utils/common/fieldlist.d	99.87% <100.00%> (ø)
tsv-summarize/src/tsv_utils/tsv-summarize.d	98.31% <100.00%> (+0.05%)	⬆️