Unify {mdoc,man}_{alloc,reset,free}() into roff_man_{alloc,reset,free}().

Unify {mdoc,man}_{alloc,reset,free}() into roff_man_{alloc,reset,free}().
Minus 80 lines of code, no functional change.
Written on the train from Koeln to Wolfsburg returning from p2k15.