Fix directory read serialization bottleneck

The directory walker used dirreadall call for loading directory
entries into memory before assigning them to workers -- causing
severe and unwanted serialization that was especially noticeable
on long directories.

The solution is simple: chunk up the directory read and assign
work in between the chunks.

Remove README

cool uris don't change

mkfile: *actually* install to /$objtype/bin; derp (thanks qwx)

mk install to the system path (alas)

fix manpage install target

update manual page SOURCE section

take it, it's yours

mkfile: install to $home/bin, as is Correct

ricing the code

fix double-free

implement -T flag that disables the safe-mode

simplify nblk calculation

fix not failing on error

implement robust cloud-scale format-agnostic parallel asynchronous ghost-copy data replication strategy

fix troff references

correctly handle partial reads

fix the write error check

remove stupid mkfile rules. (thanks BurnZeZ)

nicer exit on usage error. (thanks BurnZeZ)