The metricsgen tool parses and reads a metrics struct with various metrics
fields. Currently, the tool uses this data to generate the corresponding prometheus
and no-op constructors for use within Tendermint. The same data that is parsed
to generate the constructor can trivially be used to generate the metrics.md
documentation file. Autogenerating this file will reduce the toil of keeping this
file up to date and make it less likely for this simple file to become out of date.

• metricsgen generates markdown table output using TemplateData data
• make target added for regenerating this markdown file