libhammer - Add functions to help gather HAMMER statistics.
libhammer_get_volinfo.3 - Use commas to separate functions names.
hammer(8) - Adapt help output to latest changes.

* Also adapt hammer.8 manpage.
hammer(8) - Migration to libhammer (step 2/many)

* Migrate 'bstats' and 'iostats' directives.
* Adjust cmd_stats.c file width to 80 columns