This is a simple plugin, to provide basic (but configurable) health checks.
This is a server intercept plugin, and it takes one single  configuration
option in plugin.config, the configuration file name. 

This configuration contains one, or several, lines of the format

   <URI-path> <file-path> <mime> <file-exists-code> <file-missing-code>

The URI-path can *not* be "/" only.


Examples:

   /__hc  /var/run/ts-alive  text/plain 200  403


The content of the file, if any, is sent as the body of the response. The
existence of the file is sufficient to get an "OK" status. Performance wise,
everything is served out of memory, and it only stats / opens files as
necessary. However, the content of the status file is limited to 16KB, so
this is not a generic static file serving plugin.
