Minor feature enhancements, and portability

• Portability (affecting the CSV-RFC reader) for the Debian packaging request: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=800074. The latter greatly increases the number of platforms on which Miller has been validated.
• mlr decimate: http://johnkerl.org/miller/doc/reference.html#decimate
• Integer-preservation feature for mlr top and mlr stats1 with percentiles: If inputs are integers then corresponding outputs will be so as well (unless -F, which forces all-float output).
• mlr histogram now has a --auto option for autocomputing lower and upper limits: http://johnkerl.org/miller/doc/reference.html#histogram
• mlr uniq and mlr count-distinct now have a -n flag to show only the counts of distinct values, rather than listing all distinct values: http://johnkerl.org/miller/doc/reference.html#uniq http://johnkerl.org/miller/doc/reference.html#count-distinct
• The strlen function correctly handles UTF-8 string data.