Investigate Match Param Progress Callbacks

[iwillspeak]

Currently there is provisional support in the onig_sys API for these. Do we need to add any structured wrapper?

Split off from #75 .

[iwillspeak]

The code in question is here in onig_sys.

Add support for setting both of these callbacks on MatchParam.

[iwillspeak]

This will require modelling of the OnigCalloutArgs and access to them. I'm not sure how much of this has been stableised yet. From some poking around:

• Add a callout module which contains:
  • The CalloutArgs wrapper around the raw onig callout args pointer.
  • A Callout trait which can model something that can recive callouts. This trait should be implemented for Fn<CalloutArgs>.
• Changes to the MatchParam to allow a Callout to be registered. This will probably require storing the closure in the MatchParam and passing some raw function through to 'unpack' the Callout from the MatchParam via user data.