Add IPC round trip for string types (string, char, varchar, binary)

[asfimport]

As part this we should determine the most convenient way to model string types to avoid boilerplate code.

Reporter: Micah Kornfield / @emkornfield
Assignee: Micah Kornfield / @emkornfield

_{Note: This issue was originally created as ARROW-106. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Per discussion on ML we are going to remove varchar type. I actually had some time to work on this today, my guess is I will have a PR out early next week (based on the current amount of time I have to devote to this).

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 103
#103