bsdtar.1: Mention rar support + manual page polish (#2423)

bsdtar.1: Mention rar support + manual page polish (#2423)

I have been using this for years without realizing it decompresses rar.

+ add rar to supported decompression formats
+ use section references to link sections (this makes them clickable in
GUIs)
+ add paragraph breaks for consistent spacing
+ pdtar is not this program, so use Sy per mdoc style guide
+ do almost the same in reverse for bsdtar
+ remove parenthetical around a complete sentance

Thank you so much, this is wonderful software.

(cherry picked from commit 68238f28ee9e051be0c78f91f99b1ad2a4c74a03)