troff: import HB, HI and HX fonts from Plan 9 These font were accidentally left out, because their name conflicted with Hb, Hi and Hx fonts on case-insensitive file systems. These fonts were later renamed to longer names. Fixes #84. Change-Id: Ia0631f270a8cee6bee4337c4557837bba1a405ab Reviewed-on: https://plan9port-review.googlesource.com/2900 Reviewed-by: Russ Cox <rsc@swtch.com>