[TW-1899] give hooks the filter args and the command args

_Yanick Champoux on 2017-03-07T21:46:33Z says:_

Right now hooks get the args via, well, the `args` attribute. E.g.,

{code}
args:task something like progr sumfin
command:progress
{code}

While it's not too hard to have hooks to parse which part of args is the pre-command filter, and which part goes after, it's still tricky because of the possibility to abbreviate the command, and the keyword appearing something else on the line. It's be nice if the hooks got something like

{code}
args:task something like progr sumfin
pre_command_args: something like
post_command_args: sumfin
command:progress
{code}