[Python] Add support for FixedWidthBinary type

[asfimport]

Reporter: Wes McKinney / @wesm
Assignee: Phillip Cloud / @cpcloud

Related issues:

• Arrow 0.3 release (blocks)
• [C++] Add FixedWidthBinary type (is related to)

_{Note: This issue was originally created as ARROW-632. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 461
#461